Slow Cooker Chicken Parmesan Soup

Ingredients

• 4 garlic cloves, minced
• 1 green bell pepper, chopped
• 1/2 medium onion, chopped
• 14 1/2 oz. can crushed tomatoes
• 1/2 lb. boneless, skinless chicken breasts
• 5 c. low-sodium chicken broth, plus more if needed
• 1/2 c. shredded Parmesan cheese, plus extra for garnish
• 2 T. chopped fresh basil
• 2 t. chopped fresh oregano
• 1 t. salt
• 1/2 t. black pepper
• 1/4 t. crushed red pepper flakes
• 4 oz. penne pasta
• 2 T. unsalted butter, optional
• chopped fresh basil or parsley, for garnish