In a large skillet, brown the spicy turkey sausage. When it's just about done, add the diced peppers and onion. Saute until soft, about 5 minutes. Add garlic and cook for another minute. Drain any grease if needed, and add mixture to slow cooker.
Add the crushed tomatoes, fire-roasted tomatoes, and tomato sauce to the slow cooker.
Add the Italian seasoning and the heavy cream; give the sauce a good stir.
Add the pasta to the slow cooker and mix in, making sure all the pasta is covered with sauce.
Cover, and cook on high for about 1 1/2 hours OR on low for about 2 1/2 hours. Check pasta for doneness about half way through the cooking time. When pasta is al-dente, top with shredded mozzarella cheese and turn slow cooker to low. When cheese is melted, it's ready to serve.