HEAT grill to medium heat.
RESERVE 1/4 cup barbecue sauce for spreading onto rolls; set aside.
PLACE chops on grill; brush lightly with some of the remaining barbecue sauce. Grill 6 to 8 min. on each side or until done (160°F), brushing occasionally with remaining barbecue sauce and adding onions to the grill for the last 4 min., turning after 2 min.
SPREAD rolls with reserved sauce; fill with chops, onions, lettuce and tomatoes.