COMBINE stuffing mix, meat, egg and water. Shape into 1-inch balls. Place in slow cooker; top with mushrooms, peppers and spaghetti sauce. Cover with lid.
COOK on LOW for 6 to 8 hours (or on for HIGH 3 to 4 hours).
COOK spaghetti as directed on package; drain. Serve meatballs with sauce over spaghetti. Sprinkle with cheese.