In a small bowl, combine fajita seasoning. Set aside.
In another small bowl, whisk together 2 tablespoons of fajita seasoning with 2 tablespoons of oil, minced garlic and the juice of 1 lime. Place flank steak into a resealable bag and pour marinade in, massaging into the meat to evenly coat. Let marinate for 1 hour, or longer in the refrigerator. (If refrigerated, let meat sit at room temperature 30 minutes prior to cooking).
For Stovetop Steak
Heat a tablespoon of oil in a large cast iron or other heavy bottomed skillet or grill pan. Wipe most of the marinade off of the meat and sprinkle with salt and place in the pan. Cook for about 3 minutes per side, flipping once, for medium rare or 5-6 minutes for well done. Transfer to a plate to rest and tent with foil.
For Grilled Steak
Preheat an outdoor grill to medium high heat. Grill steak, flipping once, about 4-5 minutes per side for medium rare. Transfer to a plate and tent with foil to rest while you cook the veggies on the stovetop.
Add a tablespoon of oil to the skillet, then add the vegetables. Seasoning with remaining fajita seasoning (about 3/4 tablespoon) and a pinch of salt. Cook 5-7 minutes or until desired tenderness is reached. Squeeze lime juice over the veggies and toss.
Slice steak against the grain. Warm tortillas in the microwave or char on the stovetop. Fill with sliced steak, veggies and desired toppings. Serve with lime wedges.