In shallow dish, place chicken with mushrooms.
Cover with dressing.
Marinate for 30 minutes.
Drain; reserve dressing.
In large skillet, cook onion in margarine till tender.
Add chicken and mushrooms.
Cook, covered over med heat till chicken is tender.
Add zucchini, tomatoes and marinade.
Cook and stir until zucchini is tender.
Remove from heat.
Sprinkle with cheese pieces.
Cover and let stand 2 minutes for cheese to melt.
