Butternut Squash and Spinach Breakfast Casserole

This easy Butternut Squash and Spinach Egg Casserole is healthy, easy to make, and perfect for meal prep or a fancy brunch.  The combination of butternut squash, spinach, and feta ranks up there as one of my favorites, especially when it's all baked together in a tasty breakfast dish like this.

Lately, I have been enjoying making a big savory egg dish or breakfast casserole on Sundays that I can just use as a grab-and-go meal during the week as part of my meal planning. It makes breakfast easy and mindless, which is exactly what I need when the coffee kicks in. Plus, the protein from the eggs keeps me full all morning and I don't find myself reaching. for snacks.

The other thing I love about this is how versatile it is. Make it with different combinations of veggies, try out different cheeses, use sweet potatoes instead of butternut squash - the options are endless.

Why You'll Love This Butternut Squash Breakfast Casserole

• Nutritious: Butternut squash is rich in vitamins, minerals, and fiber. Spinach is packed with iron, antioxidants, vitamins, and minerals. Eggs are a great source of protein making this breakfast healthy, filling, and a great way to start the day.
• Versatile: Breakfast casseroles like this are so easy to customize! Switch out the veggies, add bacon or sausage, and try it with different cheeses.
• Serve it for breakfast, lunch, or dinner:  Add breakfast potatoes and turkey bacon for breakfast or salad and soup for lunch or dinner. Think of it like a frittata or quiche.

Looking for more delicious butternut squash breakfast dishes? Try this Butternut Breakfast Casserole with Sausage, this Breakfast Salad, or Breakfast Burrito Bowls (just swap butternut squash for the sweet potatoes.)

Ingredients and Substitutions

Here is everything you need for this tasty breakfast.

• Eggs: Eggs are the base of this hearty breakfast casserole. Use whole eggs, egg whites, or a combination of the two. Add a touch of milk or half and half (or cream) for a creamier consistency.
• Butternut squash: Butternut squash is the star of this dish. Use fresh peeled butternut squash or speed up prep by using frozen butternut squash cubes. Cook them right from frozen in the skillet with the onion. Just make sure to drain out any excess water. You can swap in another type of squash or sweet potatoes as well.
• Spinach: Spinach adds color, flavor, and nutrition to this recipe. Use any greens you like including kale, arugula, or cabbage. Just make sure it is fully cooked and tender.
• Onion: Red onion adds some natural sweetness and tang to this recipe. Use any onions you like or swap in green onions or shallots for a milder flavor.
• Spices: It's important to add kosher salt and pepper to eggs or they end up tasting blend. Additionally, add garlic powder (or fresh minced garlic) and oregano. Butternut squash is also delicious with sage, rosemary, or fresh herbs. 
• Cheese: Feta cheese is a great way to layer in more flavor to this dish. It's also really good with goat cheese, shredded sharp cheddar, Swiss cheese, or Parmesan. Leave out the cheese for a dairy-free option.

How to Make Butternut Squash Breakfast Casserole

Here's how to make this easy breakfast casserole.

1. Saute the butternut squash, onions, and spinach

It's important to cook the vegetables before adding them to the casserole or they will release liquid into the casserole and change the texture. Start by heating olive oil in a large skillet. Add the onion and diced butternut squash. Cook for 8-10 minutes until the butternut squash is fork tender.  Season with salt, pepper, and spices. Stir in spinach until it wilts.

Taste and season if needed, but remember that feta cheese is salty, so do not over-salt the vegetables.

If you are using frozen butternut squash, start with just the onions and add the butternut squash after the onions cook for a couple of minutes. 

Roasting option: You can also roast the butternut squash and onions at 425 degrees for 20-25 minutes until fork tender.

2. Assemble the casserole and bake

Start by whisking the eggs and feta cheese until everything is well combined. Spray a baking dish with cooking spray and then add the butternut squash, spinach, and onions. Pour the eggs over top.

Bake for 20-25 minutes until the eggs are just set. Make sure not to overcook the eggs or the casserole will taste dry. The eggs continue to cook after they come out of the oven, so don't worry if they seem slightly soft.

Ideas for Customizing Butternut Squash and Spinach Breakfast Casserole

The great thing about this meal is that there are so many ways to make it your own!

• Swap in different vegetables: Sub out the butternut squash for any other squash or veggies that you like. Asparagus, zucchini, yellow squash, or broccoli will work well here.
• Use kale: You can use kale instead of spinach — or both!
• Add more protein: Add cooked bacon, turkey sausage, chicken sausage, or beans to the casserole for more protein. 
• Egg whites: You can use some egg whites or Egg Beaters instead of whole eggs if you like.
• Add Mediterranean flavors: Add black olives, capers, artichoke hearts, or roasted red peppers to give the dish more of a Mediterranean taste.
• Add crust: Add biscuit dough to the bottom of the pan first, if you want a little bit of bread with your casserole (you might have to adjust the cooking time).
• Serve it as a breakfast sandwich: Better yet, add a slice of this casserole between two pieces of sprouted grain bread with sliced avocado for an even more nutritious breakfast.
• Make a breakfast bowl: Turn this into a breakfast bowl with greens, avocado, hot sauce or salsa, and canned black beans, rice, or quinoa.
• Turn it into butternut squash hash: If you don't feel like baking a casserole, turn this into a breakfast hash by topping the cooked butternut squash, onions, and spinach with scrambled or fried eggs. Finish with feta cheese and herbs, similar to this Hippie Hash or Sweet Potato Hash.

What Makes this Breakfast Casserole Healthy?

It's always good to start the day off on a healthy note I think. And this dish is no exception. It's chock full of healthy ingredients that all do good things for your body.

• Olive oil is a great base oil that's good for cooking with and for adding to salad dressings, marinades, and a whole lot of other foods. It provides the good kind of heart-healthy fat and antioxidants.
• Butternut squash is full of fiber, vitamin A, and potassium. It's also low calorie and has protein, iron, and vitamin C as well.
• Red onions contain flavonoids and phytochemicals which help to ward off disease, cancer, and infection.
• Spices like salt, garlic powder, oregano, and pepper not only make your food flavors soar, but they also deliver nutrients like vitamins, minerals, and anti-inflammatory properties that keep your body healthy.
• Spinach is chock full of iron; vitamins A, C, and K1; protein; and fiber and it's low-carb and low-calorie.
• Eggs provide healthy cholesterol, protein, and antioxidants, and are very filling, despite being a low-calorie food.
• Reduced-fat feta cheese is a salty cheese that has less fat than other cheeses. It also contains zinc, folate, selenium, vitamin B6, and zinc.

How To Prepare and Cook Butternut Squash

Butternut squash is tough to cut so you'll need a sharp knife and vegetable peeler. First, take off the top and bottom of the squash to make a flat surface. Then use a vegetable peeler to remove the skin. Cut the squash in half, remove the seeds, then go about dicing it up as you would any other vegetable. It will just take a little longer, but it's worth the effort.

For cooking it, you can saute it as I did here for this recipe, bake it whole like this whole roasted butternut squash,  and turn it into fries like these Butternut Squash Fries. Or, you can cook it and blend it up into butternut squash soup.

How to Use Egg Casserole in Meal Planning: Leftovers and Storage

This casserole is great for meal planning. I'll make it on Sunday and have enough servings to have it every breakfast again for the rest of the week. It's so much easier than you think and so worth the work in advance.

• Let the casserole fully cool and then cut into individual servings. Store in an airtight container for 4-5 days in the fridge. 
• East cold, room temperature, or warmed up.