In a small bowl, prepare the marinade by combining 2 tablespoons olive oil, lime juice, Worcestershire sauce, chili powder, cumin, brown sugar, salt, smoked paprika, dried oregano, black pepper, and minced garlic. Mix well.
Slice the flank steak into thin slices against the grain, about ¼ -inch thick. Place sliced steak in a large zip-top bag or a shallow dish. Pour the marinade over the steak, ensuring it is evenly coated, massaging it into the beef. Seal the bag or cover the dish with plastic wrap. Place in the fridge and allow the steak to marinate for at least 30 minutes or refrigerate overnight for maximum flavor.
When ready to prepare fajitas, heat one tablespoon of olive oil in a very large skillet over medium-high heat.
Add the thinly sliced onions and bell peppers to the skillet. Sauté them for about 10 minutes until they become tender-crisp. Remove the vegetables from the skillet and set them aside.
In the same skillet, add another tablespoon of olive oil. Remove the steak from the marinade, and place the steak in the skillet. It’s best to do this in batches so that the meat browns rather than steams. Cook the steak over medium high heat for about 3 to 5 minutes per side for medium-rare, or adjust the cooking time according to your preference. Repeat with remaining steak if doing in batches.
Once the steak is cooked to your desired doneness, add the sautéed onions and bell peppers back into the skillet with the steak. Stir everything together and cook for an additional minute to reheat the vegetables.
Remove the skillet from heat and let the fajita mixture rest for a few minutes.
If desired, warm the tortillas in a separate skillet or using your preferred method.
Serve the steak fajitas by placing a spoonful of the fajita mixture on a warm tortilla. Add desired toppings, such as guacamole, sour cream, shredded cheese, salsa, or chopped cilantro.
Notes
If desired, use 2 tablespoons of fajita seasoning instead of chili powder, cumin, brown sugar, salt, smoked paprika, dried oregano, and black pepper.
You can customize this recipe by adding other toppings such as sliced avocado, diced tomatoes, or jalapenos according to your preference.
For spicier fajitas, add ¼ - ½ teaspoon cayenne powder to marinade.
Nutrition information is for 3 fajitas made with small flour tortillas, and doesn't include optional toppings.