HEAT oven to 425°F.
ADD broccoli and carrots to saucepan of boiling water; cook 2 to 3 min. or until crisp-tender. Drain, reserving 1/4 cup cooking water. Meanwhile, mix next 3 ingredients until blended.
RETURN cooked vegetables to saucepan. Add cream cheese mixture and onions; stir until vegetables are evenly coated with sauce, adding reserved cooking water if necessary for desired consistency.
SPOON into 2-qt. casserole sprayed with cooking spray; top with shredded cheese and bacon. Cover.
BAKE 25 min. or until heated through, uncovering for the last 5 min.