In a shallow, nonmetallic dish combine orange juice, soy sauce, honey, lemon-pepper seasoning, ginger, and garlic powder. Set aside.
Place each chicken breast half between 2 pieces of plastic wrap. Working from center to the edges, pound lightly with the flat side of a meat mallet to an even thickness. Remove plastic wrap. Place chicken pieces in marinade. Cover and chill for 4 to 6 hours or overnight.
Remove chicken from marinade, reserving marinade. To grill, place chicken on an uncovered grill directly over medium coals. Grill about 12 minutes or until tender and no longer pink, turning and brushing chicken with marinade once. Discard any remaining marinade. (Or, place chicken on the unheated rack of a broiler pan. Broil 4 to 5 inches from heat about 7 minutes, turning and brushing chicken with marinade once.)
Split buns and place on grill rack or broiler pan for 1 to 2 minutes to toast. Serve chicken breasts on toasted buns. Top each with lettuce and tomato slices. Makes 4 servings.