COOK and stir peppers and onions in large nonstick skillet sprayed with cooking spray on medium heat 5 min. Add zucchini; cook and stir 2 min.
STIR in spaghetti sauce; cover. Cook 8 min. or until vegetables are crisp-tender, stirring occasionally.
SPRINKLE with cheeses; cook, covered, 1 min. or until mozzarella is melted.