RESERVE 1/4 cup barbecue sauce. Pour lime juice over chops in shallow dish; refrigerate 10 min.
HEAT grill to medium heat. Remove chops from juice; discard juice. Grill chops 3 min. on each side. Brush with half the remaining barbecue sauce. Grill 2 to 3 min. on each side or until chops are done (145°F), brushing occasionally with remaining barbecue sauce. Remove chops from grill; let stand 3 min. Meanwhile, grill onions 2 min. on each side.
SPREAD rolls with reserved sauce; fill with chops, onions, lettuce and tomatoes.