Heat oven to 400°F. In small bowl, combine oil, basil, oregano, salt, garlic powder and pepper; mix well.
In ungreased 13x9-inch (3-quart) baking dish, arrange mushrooms, tomatoes and onions; brush with about half of oil mixture. Arrange chicken over vegetables. Brush with remaining oil mixture.
Bake at 400°F. for 50 to 60 minutes or until chicken is fork-tender and juices run clear, spooning pan juices over chicken once during baking. Serve chicken and vegetables with pan juices.