Slice meat against the grain 1/2 inch slices.
Toss the sliced steak in a ziplock with all of the seasonings. Allow to marinate in the refrigerator for 2 hours.
Slice the onion and bell peppers and keep in a bowl until you're ready to cook your fajitas.
30 minutes prior to eating, preheat your cast iron skillet to medium-high heat.
Add 2 tablespoons of olive oil to your pan and sear your meat. Try to let it fully cook on one side (2-3 minutes) before flipping so you get nice flavor.
Remove your meat to a dish and sauté your veggies in the juices. Add another tablespoon of oil, if needed.
Cook your onions and peppers (sprinkle with salt and pepper to taste) until they are tender, but not mushy.
Add in the meat to get the fajita fillings married and to warm the meat.