Turn stovetop setting to HIGH.
Add oil to insert.
Add Italian sausage, and cook until browned. Drain grease if desired.
Stir in onion and peppers, and cook until vegetables are softened.
Add garlic, Italian seasoning, and basil. Stir in to combine.
Stir in crushed tomatoes, diced tomatoes, and heavy cream.
Season with salt and pepper.
Add ziti to insert, and nestle into the sauce.
Pour tomato sauce over pasta, and make sure that noodles are covered in sauce.
Turn slow cooker setting to HIGH. Cover, and cook for 3 hours.
Gently stir pasta.
Sprinkle mozzarella over pasta. Cover, and let melt.