In 3- to 4-quart slow cooker, place chicken. Top with soup, mushrooms and water; stir gently to mix and spread evenly over chicken.
Cover; cook on Low heat setting 4 1/2 to 5 1/2 hours.
About 15 minutes before serving, stir thawed peas and the rice into chicken mixture. Cover; cook on Low heat setting 10 to 15 minutes longer or until rice is tender. If desired, add salt and pepper to taste.