To make the dressing: Combine all ingredients in a food processor or blender. Puree for 15 seconds. Place into a dressing container or mason jar and store in the fridge for up to 2 weeks. You can also add a couple of tablepssons of salsa or pico de gallo to the dressing for even more flavor.
Preheat the oven to 375*. Let the steak come to room temp. Heat a cast-iron skillet over medium-high heat for 5 minutes. Meanwhile, rub butter over both sides of the steak. Generously rub steak with seasoning. Add the grapeseed oil to the skillet. Place steak into the cast iron skillet and cook 2 minutes per side. Turn off the heat. Place cast iron into the oven for 5 minutes for rare, 6 minutes for medium-rare, or 7 minutes for medium. Remove from the oven and place on a cutting board. Let rest for 5 minutes. Slice steak into strips.