Preheat oven to 375 degrees. Arrange eggplant, onions, and zucchini on a baking sheet, sprayed with cooking spray. Lightly spray top of vegetables with cooking spray as well. Cover with aluminum foil. Bake for 10 minutes covered and 10 minutes uncovered.
Heat oil in a large nonstick pan. Add chicken, and sauté for about 3 minutes or until lightly browned.
Add zucchini, eggplant, onion, green pepper, and mushrooms. Cook for about 15 minutes, stirring occasionally.