PREHEAT grill to medium-high heat. Mix meat, onions, garlic, salt and pepper. Shape into four 1/2-inch-thick oval patties.
GRILL patties 5 min. Brush with 2 Tbsp. of the barbecue sauce; turn over. Continue grilling 5 min. or until medium doneness (160°F).
REMOVE patties from grill. Top evenly with the remaining 2 Tbsp. barbecue sauce.