In a large Dutch oven, heat the oil from the sun-dried tomatoes over medium heat. Add the chopped yellow onion and minced garlic, stirring frequently until the onion turns translucent and fragrant, about 3–4 minutes.

Stir in the tomato paste and sun-dried tomatoes, allowing them to cook for about 2 minutes. Stir continuously, watching as the tomato paste darkens slightly.

Pour in the chicken broth and add the heavy whipping cream, fresh basil, kosher salt, dried Italian seasoning, garlic powder, and crushed red pepper. Bring to a vigorous boil, then reduce heat and let it simmer for approximately 12 minutes.

Add the medium shell pasta and cook it until tender, about 12 minutes, stirring occasionally.

Reduce the heat further and gently stir in the fresh baby spinach, shredded rotisserie chicken, cream cheese, and grated Parmesan cheese, allowing to warm through and melt, about 5 minutes.

Ladle the soup into bowls and garnish with extra Parmesan cheese, fresh basil, and crushed red pepper flakes.