Bring a large pot of water to a boil with the potatoes. Cook for 8-12 minutes until they are just beginning to soften. You should be able to pierce them with a fork. Drain and lightly dry with a towel.
Heat the oil over medium high heat in a heavy skillet. Add the potatoes in a single layer and season well with salt and pepper. Cook for 10-12 minutes. Let them cook and brown on one side and then gently flip or stir. They should be lightly crispy on all sides. Remove and set aside.
Add the beef to the skillet (with some oil if needed) in a single layer. Season with salt and pepper. Cook for 4-6 minutes until cooked to your liking. Let it brown on one side before stirring or flipping. Do not overcook or crowd the pan or the steak will become tough and chewy.
Add the tomatoes and garlic and cook for 1 minute until fragrant. Add the tomato sauce, and cumin. Cook for 3-5 minutes until tomatoes are softened and a sauce is forming. Season with salt and pepper if needed.