Start by heating the sun-dried tomato oil in a large Dutch oven over medium heat. Toss in the onions and garlic, stirring frequently until they become soft and aromatic. Next, stir in the tomato paste and sun-dried tomatoes for a couple of minutes to deepen the flavor.
Pour in the chicken broth, heavy cream, and seasonings (Italian seasoning, garlic powder, and crushed red pepper). Bring the mixture to a boil, then reduce the heat to a gentle simmer. This creates a rich and creamy base for the soup.
Add the pasta shells to the simmering broth. Stir occasionally to prevent sticking and cook until the shells are just al dente. This usually takes about 10-12 minutes.
Lower the heat and fold in the fresh spinach, shredded chicken, cream cheese, and Parmesan. Simmer gently and stir often to melt the cheeses smoothly into the broth. Taste and adjust the seasonings if needed.
Ladle the soup into bowls and garnish with extra Parmesan, fresh basil, and a pinch of red pepper flakes for that finishing touch. Serve immediately!