To a large pan on the stove over medium heat add the sausage and onion break the sausage up and cook it through.

Remove any excess grease from the pan. Add in the diced tomatoes, marinara sauce, water and seasonings. Stir well, add 1/2 of this sauce mixture to the bottom of your slow cooker, sprinkle half of the cheddar cheese and Parmesan cheese on the top, place the spaghetti noodles over the cheeses, then pour the remaining sauce mixture over the noodles. Make sure the noodles are covered then sprinkle with the remaining cheeses. Cover with a lid and cook on low for 3-4 hours or until the spaghetti noodles are tender.