Mix together first 7 ingredients for the marinade.
Place steak and vegetables in a large ziplock bag. Pour marinade in bag. Mix well and make sure everything is coated and marinade is evenly distributed. Marinade in refrigerator for at least two hours or overnight.
Let beef and veggies marinate at room temperature for at least an hour before cooking. Drain well before cooking.
Heat a large, well-seasoned cast iron skillet until it's smoking hot. Add a tablespoon of bacon grease. Place skirt steak in skillet and sear for two minutes on each side. Remove from skillet and cover with aluminum foil and let rest while the vegetables are cooking.
Add more oil to the skillet if necessary. Throw the veggies in the hot skillet and cook for about 5 minutes, stirring frequently, or until the vegetables are tender.
Remove skillet from heat and scoot the vegetables over to one side to make room for the steak.
Slice steak on the diagonal in thin strips. Return to hot skillet.
The best part about fajitas is serving right from the skillet. In fact, I do believe that's the law.
To assemble fajitas, place a small amount of the beef/vegetable mixture in the center of a tortilla and small amounts of desired toppings. Roll up the tortilla, pick it up with your hands and eat!