In a large mixing bowl, combine the diced onions, minced garlic, chicken broth, diced tomatoes (with juice), Italian seasoning, salt, and black pepper. Stir well to combine.
Place the chicken breasts in the bottom of the crock pot. Pour the broth mixture over the chicken, making sure the chicken is well coated.
Cover the crock pot with the lid and set it to cook on low for about 6 hours.
After 6 hours, remove the chicken from the crock pot. Shred the chicken using two forks, then return the shredded chicken to the pot.
Stir in the heavy cream and grated Parmesan cheese. Add the uncooked pasta, mixing it in well. Cover the pot again and cook for an additional 30-60 minutes on low, until the pasta is tender.
Once the pasta is cooked, give the soup a good stir. Taste and adjust the seasoning if necessary.
Serve hot, garnished with fresh basil or parsley if desired.