In a skillet, brown the ground Italian sausage then drain.
Place the browned Italian sausage into the base of the slow cooker and add the tortellini (fresh or frozen), marinara, beef stock, salt, pepper, and Italian seasoning. Gently stir through.
Set the slow cooker on low and cook for 1 hour. At the end of the cooking cycle, stir the grated Parmesan cheese into the sauce, and then top with shredded mozzarella cheese.
Serve Slow Cooker Italian Tortellini with side salad.