HEAT large nonstick skillet on medium-high heat. Add chicken; cover skillet with lid. Cook 5 to 7 min. on each side or until chicken is done (165ºF), adding onions and zucchini after 5 min.
ADD dressing, tomatoes and olives; cover. Cook on medium-low heat 2 min. or until heated through; stir.
TOP with cheese; cook, covered, 2 min. or until melted.