Preheat oven to 450 degrees F. Spray a large baking sheet with non-stick spray.
Place flank steak in the center of baking sheet. Drizzle 1/2 Tablespoon of vegetable oil over the steak.
Mix together chili powder, ground cumin, paprika, salt and pepper. Sprinkle this mixture evenly over the top of the steak. Rub the spice mixture into the steak. Sprinkle minced garlic over the top.
Cut each bell pepper and the red onion into thin 1/4 inch strips. Spread them all around the sides of steak. Drizzle the remaining vegetable oil all over the peppers and onion.
Bake in preheated oven for 12 to 15 minutes or until steak reaches desired doneness. Using a meat thermometer check for meat temperature. 140 degrees F is medium rare. 150 is medium. and so on. (I cooked mine for about 17 minutes which made them almost well done.)
Remove from oven. Squeeze the juice of one or two limes evenly over steak, peppers and onion.
Let steak stand 10 minutes before slicing. *This is important to keep the steak tender. Then cut steak into thin slices against the grain.
Serve steak, peppers in onion inside warm tortillas and top with favorite toppings. Enjoy!