Layer the Base – In the bottom of your slow cooker, add the diced onions, minced garlic, crushed tomatoes, diced tomatoes, Italian seasoning, salt, pepper, and red pepper flakes. Stir to combine and nestle in the chicken breasts.

Add the Broth and Cook – Pour in the chicken broth, making sure everything is covered. Set your crockpot to cook on low for 6–7 hours or high for 3–4 hours.

Shred the Chicken – Once the chicken is cooked through and tender, use two forks to shred it directly in the pot. It should fall apart easily.

Add Pasta – Stir in the uncooked pasta and continue cooking on high for 15–20 minutes, or until the pasta is al dente. Stir occasionally to prevent sticking.

Cheese It Up – Once the pasta is cooked, stir in the grated parmesan and shredded mozzarella cheese. Let it melt into the soup, creating a creamy, cheesy consistency.

Serve and Garnish – Ladle the soup into bowls and top with more cheese, fresh basil or parsley, and a sprinkle of crushed red pepper if you like a little heat.