In a slow cooker, stir together garlic, bell pepper, onion, diced tomatoes, chicken breasts, chicken broth, Parmesan cheese, Italian seasoning, and ground red pepper. Cook on high for 3 1/2 hours or on low for 7 hours.
Transfer the chicken to a cutting board and shred into small pieces. Return chicken to slow cooker and stir in pasta. Cook on high 30 minutes.
At this time, if the soup is too thick, add some additional chicken broth and warm through.
Serve garnished with shredded mozzarella cheese and chopped parsley.