To naturally tenderize a lean cut of meat like flank steak, score and marinate it before grilling.
Score meat by making shallow cuts at 1-inch intervals diagonally across steak in a diamond pattern. Repeat on the other side. Place meat in a plastic bag set in a shallow dish. For marinade, stir together orange juice concentrate, tequila or water, lime juice, gingerroot, oregano, salt, ground red pepper, and garlic. Pour over meat in bag. Close bag. Marinate 30 minutes at room temperature or in the refrigerator up to 4 hours, turning bag occasionally.
Drain meat, reserving marinade. Place meat on the unheated rack of a broiler pan. Broil meat 3 inches from the heat for 12 to 14 minutes or until desired doneness (145 degrees F for medium-rare doneness), turning once. [Or, grill meat on an uncovered grill directly over medium coals for 12 to 14 minutes or until desired doneness (145 degrees F for medium-rare doneness), turning once.] Thinly slice meat diagonally across the grain.
To warm tortillas, wrap in foil. Place beside broiler pan or on grill rack for the last 8 minutes of cooking meat.
Meanwhile, pour reserved marinade into a small saucepan. Stir in sweet pepper strips and onion. Bring to boiling; reduce heat. Simmer, uncovered, for 3 to 5 minutes or until vegetables are tender.
To serve, immediately fill warmed tortillas with beef. Using a slotted spoon, spoon pepper-onion mixture over beef. If desired, sprinkle with chili peppers. Roll up fajitas. Makes 4 servings.