Trim the excess fat from the meat and cut it crosswise into long strips about 1/2 inch wide. Place the strips in a shallow, nonreactive dish. In a bowl stir together the lime juice, 1/3 cup oil, tequila, cumin, oregano, pepper and garlic. Pour over meat, coating each piece well.
Cover with plastic wrap and refrigerate for 24 hours, turning the meat over a few times. In a heavy frying pan or a griddle over medium heat, warm the 1 tablespoon oil. Cook the onion, stirring, until well browned, 6 to 8 minutes. Transfer to a plate and keep warm.
Place the same pan or griddle over high heat. Drain the meat well, reserving the marinade. Add the meat to the pan or griddle and cook, turning once and basting with the leftover marinade, until done to your liking, about 2 minutes on each side for medium-rare. Transfer to the plate holding the onions and keep warm.
Heat the tortillas, turning once, on the same pan or griddle, about 10 seconds on each side. Alternatively, wrap in plastic wrap and place in microwave oven for about 30 seconds. Just before serving gently heat the refried beans in heavy saucepan. Cover and keep warm. Arrange the meat, onions and tortillas on a warmed platter. Place the refried beans, guacamole, salsa, sour cream and cilantro in separate dishes on the side. Diners can prepare their own fajita according to their liking.