Arrange onion and apple slices in bottom of slow cooker. Place chicken pieces on top and season all over with salt and black pepper. Sprinkle rosemary over chicken.
In a medium bowl, whisk together chicken stock and soup. Pour mixture over chicken.
Cover and cook on LOW for 6 to 8 hours or on HIGH for 3 to 4 hours.
Serve chicken, sauce, apples, and onions over rice.