PREHEAT grill to medium-high heat. Spray both sides of onion slices with cooking spray; set aside. Mix meat and 1/4 cup of the steak sauce; shape into four 1/2-inch-thick patties.
GRILL patties 5 min.; turn. Add onions to grill. Cook burgers an additional 5 min. or until cooked through (160ºF), brushing occasionally with the remaining 1/4 cup steak sauce and turning onions after 3 min.
PLACE burgers on bottom halves of rolls; cover with onions and tops of rolls.