COOK chicken in large nonstick skillet on medium-high heat 5 to 7 min. on each side or until done (165ºF). Transfer to platter; cover to keep warm.
ADD dressing, zucchini and onions to skillet; cook on medium heat 4 min. or until vegetables are crisp-tender, stirring occasionally. Stir in tomatoes and snow peas; cook 1 to 2 min. or until heated through.
TOP chicken with vegetable mixture and cheese.