PREHEAT grill to medium heat. Reserve 1/4 cup of the barbecue sauce for spreading onto rolls; set aside. Place steaks on grill; brush with some of the remaining barbecue sauce.

GRILL steaks 6 to 8 min. on each side or until cooked through (160°F), brushing occasionally with remaining barbecue sauce. Add onions to grill during the last 4 min. of meat grilling time, turning after 2 min.

SPREAD cut sides of rolls with reserved 1/4 cup barbecue sauce. Fill with steaks, onions, lettuce and tomatoes.