Coat a large skillet with nonstick spray. Add mushrooms and onion. Cook over medium heat 5 minutes. Remove from heat. Add spinach and the 1 tablespoon water to skillet. Cover; cook 1 minute until spinach just wilts.
Stir in the cooked chicken and heat through. Add cheeses and salad dressing; toss. Serve with pitas. Makes 4 servings.
You can omit the cooked spinach and serve the cooked chicken mixture over torn fresh spinach on pitas.