HEAT grill to medium heat.
PLACE peppers, onions and dressing in center of sheet of heavy-duty foil sprayed with cooking spray. Fold to make packet.
GRILL 15 min. or until vegetables are tender, turning packet occasionally. Meanwhile, grill franks 8 to 10 min. or until heated through (160°F), turning occasionally.
FILL buns with franks; top with pepper mixture.