PREHEAT greased grill to medium-high heat. Mix meat, onions and garlic; shape into four patties.
GRILL patties 8 min. Turn patties; brush with 1/4 cup of the barbecue sauce. Grill 4 min. or until patties are cooked through (160°F). Brush cut sides of buns with remaining 1/4 cup barbecue sauce; place, cut-sides down, on grill. Grill 1 to 2 min. or until buns are lightly toasted. Top each patty with 1 cheese slice; grill an additional 1 min. or until cheese begins to melt.
COVER bottom halves of buns with lettuce and tomatoes; top with cheeseburgers and tops of buns.