Heat dressing in large skillet on medium heat. Add chicken; sprinkle with 1/4 tsp. black pepper. Cook 2 to 3 min. on each side or until evenly browned on both sides. Remove chicken from skillet, reserving drippings in skillet; cover chicken to keep warm. Add mushrooms, onions, green peppers and garlic to skillet; cook and stir 5 min. or until onions are crisp-tender.