Place chicken breasts in the bottom of a 5-6 quart slow cooker.
Add diced onion, garlic, crushed tomatoes, pasta sauce, chicken broth, tomato paste, Italian seasoning, basil, oregano, red pepper flakes, garlic powder, salt and pepper. Stir to combine.
Cover and cook on low for 6-7 hours or high for 3-4 hours until chicken is fully cooked and tender.
Remove chicken from slow cooker and shred with two forks. Return shredded chicken to the pot.
About 30 minutes before serving, stir in uncooked pasta. Cook on high until pasta is tender, 20-30 minutes. Add extra broth if soup becomes too thick.
Stir in heavy cream and Parmesan cheese until melted and combined. Taste and adjust seasonings as needed.
Serve topped with shredded mozzarella cheese and fresh basil or parsley.
Notes
Can use rotisserie chicken for quicker prep – add with pasta and skip slow cooking step.
Pasta will absorb liquid over time – add more broth when reheating.
Can use any short pasta shape like rotini, penne, or shells.
For creamier soup, add cream cheese along with heavy cream.