HEAT grill to medium heat.
MIX meat and 2 Tbsp. barbecue sauce just until blended; shape into 4 (1/2-inch-thick) patties.
GRILL 5 to 6 min. on each side or until done (160°F). Top with cheese; grill 1 min. or until melted.
SPREAD buns with remaining barbecue sauce; fill with cheeseburgers, bacon bits, onions and tomatoes.