In a medium bowl combine the guacamole ingredients and stir with a fork until thoroughly combined. Cover the surface with plastic wrap until ready to use.
In a blender or food processor finely chop the garlic and cilantro. Add the remaining marinade ingredients. Process until smooth.
Put the flank steak in one medium bowl and the chicken thighs in another. Add half the marinade to the steak and half to the chicken and turn to coat all sides evenly. Cover and refrigerate for 1 to 2 hours.
Prepare the grill for direct cooking over for medium heat (350° to 450°F).
Lightly coat the bell peppers and onions on both sides with oil. Brush the cooking grates clean. Grill them over direct medium heat, with the lid closed as much as possible, until tender, turning once and swapping their positions as needed for even cooking. The bell peppers will take 6 to 8 minutes, and the onions will take 8 to 10 minutes. Cut the bell peppers and onions into ⅓-inch strips.
Remove the steak and chicken from their bowls and discard the marinade. Grill them over direct medium heat, with the lid closed as much as possible, until the steak is medium rare and the chicken is brown on the surface and no longer pink in the middle, 8 to 10 minutes, turning once and swapping their positions as needed for even cooking. Let the steak rest for 2 to 3 minutes. Evenly divide the tortillas into two foil packets and grill over direct medium heat to warm them, 2 to 3 minutes, turning once.
Cut the steak in half lengthwise and then cut crosswise into ¼-inch slices. Cut the chicken into ¼-inch slices. Place the tortillas, steak, chicken, peppers, onions, guacamole, and salsa in separate serving dishes. Let each person make their own fajita by placing the fillings down the center of each tortilla and adding Tabasco® sauce. Serve warm.