Place the chicken breasts in the bottom of the crockpot.
Pour the spaghetti sauce over the chicken.
Add the diced tomatoes, onion, bell pepper, and garlic.
Season with salt and pepper to taste.
Cover and cook on low for 6-8 hours or high for 3-4 hours.
Once cooked, shred the chicken using two forks.
Break the spaghetti in half and stir it into the sauce mixture.
Cover and cook on high for an additional 30 minutes until spaghetti is tender.
Stir in the mozzarella cheese until melted and well combined.
Garnish with fresh parsley before serving.