1In small bowl, mix dressing and mustard. In 3 1/2- to 4-quart slow cooker, arrange potato slices in even layer; drizzle with one-third of the dressing mixture. Arrange onion slices on potatoes; drizzle with one-third of the dressing mixture. Top with carrots and cabbage; drizzle with remaining dressing mixture.
2Arrange sausage slices on vegetables. Pour tomatoes in even layer over sausage.
3Cover; cook on Low heat setting 7 to 8 hours.