Cook cauliflower in boiling water in large saucepan 3 to 4 min. or until crisp-tender, adding corn to the boiling water for the last minute. Drain, reserving 1/4 cup cooking water.
Mix cream cheese, milk, Parmesan and garlic powder until blended. Place cauliflower mixture in 13x9-inch baking dish sprayed with cooking spray. Add peppers and cream cheese mixture; stir until vegetables are evenly coated with sauce, adding reserved cooking water if necessary for desired consistency.
Mix cracker crumbs, shredded cheese and parsley; sprinkle over vegetable mixture. Cover.
Bake 30 to 35 min. or until vegetable mixture is heated through and topping is lightly browned, uncovering for the last 10 min.