Melt the butter in a large pot over medium heat and sauté the onion until translucent.
Add the minced garlic, Italian seasoning, salt, pepper, and chili flakes, stirring until fragrant.
Pour in the chicken broth, add the raw chicken breasts, and bring the mixture to a gentle boil.
Reduce heat and simmer until the chicken is cooked through, then remove the chicken to shred it.
Return the shredded chicken to the pot and add the sun-dried tomatoes and pasta; cook until the noodles are al dente.
Whisk the cornstarch into the half-and-half and stir it into the boiling soup until thickened.
Stir in the fresh spinach and cook until wilted.
Serve hot, finished with a generous topping of ricotta, Parmesan, and mozzarella.