Cut steak crosswise into 12 lengths. Mix lime juice, oil, tequila, garlic, cumin, oregano & pepper and marinate meat and onion halves in mixture overnight or at least 4 hours. Pre-cook onion halves until partly done. Grill onions and meat on indoor or outdoor grill until meat is rare to medium (do not overcook), and onions are soft. Keep warm. Heat tortillas either on grill or in microwave unitl soft and warm. Have garnishes assembled: Salsa, guacamole, sour cream, cilantro, etc. Each person assembles their own -- meat slices down center of warm tortilla, garnishes on top, fold up bottom, fold sides up to enclose filling, eat out of hand.