In a 1-gallon zip-lock plastic bag, combine lime juice, tequila, oil, cumin, oregano, 6 tablespoons hot sauce, and garlic. Add chicken and onions, seal, and chill at least 15 minutes or up to 2 hours, turning occasionally.
Combine tomatoes and 1/4 teaspoon to 1 1/2 teaspoons hot sauce; set aside.
Oil a barbecue grill over a solid bed of hot coals or gas grill on high heat (you can hold your hand at grill level only 2 to 3 seconds). Lift onions from marinade and place on grill. Close lid on gas grill. Cook onions for 3 minutes, turn, cook a couple more minutes, then turn over and baste with marinade.
Lift chicken from marinade and place on grill; close gas grill. Turn and baste chicken and onions occasionally until onions are soft and browned and meat is no longer pink in thickest part (cut to test), about 8 minutes. Transfer chicken and onions to a board and keep warm.
Heat tortillas on grill, turning once, until softened and lightly speckled brown, 30 to 60 seconds.
Slice chicken crosswise. Place portions of chicken, onions, and beans in tortillas. Top with tomatoes, sour cream, and a squeeze of lime. Fold up bottom of tortillas, then fold in sides.
Nutritional analysis per fajita.