HEAT grill to medium heat.
PLACE peppers and onions in center of large sheet heavy-duty foil. Drizzle with dressing; fold to make packet.
GRILL 15 min. or until vegetables are crisp-tender, adding franks to the grill after 6 min. and cooking until franks are heated through, turning packet and franks occasionally.
CUT slits in foil to release steam before opening packet. Place franks in buns; top with vegetable mixture.