In large crockpot, add carrots, celery, onion, garlic, tomato sauce, chicken broth, Italian seasoning, salt and pepper. Stir.
Add chicken and make sure it's covered with the sauce.
Cover and cook on High heat for 3-4 hours or on Low heat for 6-8 hours.
Remove chicken from the crockpot and shred, using 2 forks and discarding the bones, if necessary. Switch slow cooker to High (if it was on Low heat) and add shredded chicken back.
Break spaghetti noodles in half and give a few stirs to separate the noodles and mix with the sauce and chicken. Cover and cook for about 30 minutes (less amount for gluten free spaghetti, especially brown rice). Then stir to make sure top noodles are covered with liquid, cover and cook for another 10 minutes or until spaghetti is cooked.
Sprinkle chicken spaghetti with Parmesan cheese and parsley, stir and serve hot.
Video
Notes
Store: Refrigerate in airtight container for up to 3 days.
Freeze: I don't recommend to freeze this dish as pasta doesn't freeze and thaw well. You can always cut recipe in half to avoid leftovers.