Add the sliced smoked sausage, white beans, chicken broth, diced onion, minced garlic, Italian seasoning, salt, and black pepper to the slow cooker.
Stir once to combine everything evenly.
Cover and cook on low for 6 hours or on high for 3 hours.
Stir in the fresh spinach during the last 10 minutes of cooking so it wilts without losing its color.
Ladle into bowls and top each serving with grated Parmesan cheese.