HEAT 2 Tbsp. dressing in large skillet on medium heat. Add chicken; cook and stir 4 min. or until done.
ADD onions and 1/4 cup of the remaining dressing; cook 2 min., stirring occasionally. Add mushrooms, zucchini and remaining dressing; simmer on medium-low heat 8 min. or until liquid is absorbed. Stir in mayo.
SPOON chicken mixture over pasta; top with cheese.