Add the sausage to a large skillet over medium heat and brown. Once cooked through, remove any grease from the pan.
Add the sausage to a large slow cooker along with the diced onion, minced garlic, diced tomatoes, seasonings, marinara sauce, and water. Stir well.
Cook on LOW for 7 hours or HIGH for 4 hours.
Turn slow cooker to high and stir in the uncooked pasta. Let cook for an additional 16-35 minutes or until the pasta is cooked. This may vary depending on your slow cooker. Sprinkle the cheese on top and stir in once melted. Serve and enjoy!