Combine onion, potatoes, and sausage in large skillet and cook over medium heat until sausage is no longer pink. Season with salt, pepper and italian seasoning.
Add minced garlic, beans, tomatoes and mushrooms and cook for about 5 minutes.
Add broth to a slow cooker and contents of the skillet. Cook on low heat for about 4 hours. Add the spinach and tortellini and let cook for about 30 more minutes. Garnish with parmesan cheese, if desired.