Flank Steak Fajitas Recipe

Combine all marinade ingredients in a large measuring cup. Whisk and set aside.
Find the natural graining running through the flank steak and slice against the grain into 1/4-1/2 inch strips. This is critical for tenderness. Place the steak in a large plastic Ziploc bag or sealed container and pour the marinade over the steak. Marinate for at least 2 hours and up to 24 hours. Keep refrigerated and remove 30 minutes prior to cooking.
Combine peppers, onions, oil, paprika, and cumin in a large bowl. Toss to mix.
Heat a dash of oil over medium heat in a cast iron skillet. Add peppers and onions and season all over with salt and pepper. Cook until tender and slightly charred on the edges, about 10-15 minutes. Toss every few minutes to mix and prevent burning.
Remove peppers and onions from the skillet and place on a plate. Cover with foil to keep warm.

Turn the heat up to medium-high and add flank steak to the skillet, leaving behind as much of the marinade as possible. Discard and do not reuse. Cook steak, tossing frequently until cooked through and slightly pink in the center. The steak will fully cook in about 5-7 minutes.
Move steak to one side of the skillet and return the peppers and onions to the skillet. Serve immediately with sour cream, cilantro, lime wedges, hot sauce, and warm/toasted tortillas. See the note below on toasting tortillas!