Vaqueros -- ranch hands and cowboys from the north of Mexico -- created fajitas as a way to use the flavorful and inexpensive cut of meat known as skirt steak, and Tex-Mex food enthusiasts have been grateful ever since. While the beef for modern fajitas is often pan-seared in a skillet, traditional fajitas require grilling for both the beef and the vegetables. It's a quick and simple procedure that yields restaurant-quality grilled beef fajitas at a fraction of the cost.
Combine 1/4 cup lime juice, oil, minced garlic, Worcestershire sauce, chili powder, salt and pepper in the shallow glass baking dish. Add the skirt steak and turn over to coat the meat completely. Cover with plastic wrap and refrigerate overnight or up to 24 hours.
Heat a charcoal or gas grill to high. Remove the skirt steak from the marinade, dry with paper towels and grill on one side for six minutes. Turn the steak over and grill on the other side, two minutes for medium-rare, approximately four minutes for medium and up to six minutes for well-done. The Food and Drug Administration recommends that beef cooks to an internal temperature of 145 degrees Fahrenheit.
Place the grilled steak on a carving board, sprinkle it with 1/4 cup lime juice and leave it to rest undisturbed, tented loosely with aluminum foil.
Grill the skewered red onions and red bell peppers for four to five minutes. Turn each over and grill for four to seven more minutes, until the vegetables are charred and softened. Remove them from the grill and set aside.
Place the flour tortillas on the grill and heat them for 15 seconds on each side.
Slice the skirt steak against the grain as thinly as possible and serve with the tortillas, vegetables and toppings like pickled jalapenos, shredded cheddar cheese, salsa and guacamole.