Spray 3- to 4-quart slow cooker with cooking spray. In cooker, place potatoes, carrots and thawed onions. Sprinkle chicken with salt and pepper; place over vegetables in cooker. Pour gravy over top.
Cover; cook on Low heat setting 8 to 10 hours.
Stir in thawed peas. Increase heat setting to High. Cover; cook about 15 minutes longer or until peas are tender.