Sauté Aromatics: In a large pot or Dutch oven, heat the olive oil over medium heat. Add the chopped onion and cook until translucent, about 5 minutes. Stir in the minced garlic and chopped sun-dried tomatoes; cook for an additional 2 minutes until fragrant.

Add Broth and Seasonings: Pour in the chicken broth, then add the Italian seasoning and crushed red pepper flakes, if using. Bring the mixture to a boil.

Cook Pasta: Once boiling, add the uncooked pasta shells. Reduce the heat to a simmer and cook according to the pasta package instructions until al dente, typically 8-10 minutes. Stir occasionally to prevent sticking.

Incorporate Chicken and Cream: Add the shredded cooked chicken to the pot, followed by the heavy cream and grated Parmesan cheese. Stir until the cheese has melted and the soup is creamy.

Add Spinach: Stir in the fresh baby spinach and cook for 2-3 minutes until wilted.

Season and Serve: Taste and adjust seasoning with salt and freshly ground black pepper as needed. Ladle the soup into bowls and garnish with fresh basil and additional Parmesan cheese. Serve immediately.