HEAT grill to medium-high heat.
SHAPE meat into 8 thin patties. Reserve half the cheese and bacon. Top 4 patties with remaining cheese and bacon; cover with remaining patties. Pinch edges together to seal.
GRILL 5 to 7 min. on each side or until done (160ºF), brushing occasionally the last few minutes with barbecue sauce.
SPREAD bottom halves of buns with dressing. Fill buns with burgers, remaining cheese, bacon and onions.