Sauté the Aromatics
Heat 1 tablespoon of oil from the sun-dried tomato jar in a large Dutch oven over medium heat.
Add chopped onion and minced garlic. Sauté, stirring frequently, until softened, about 3–4 minutes.
Cook the Tomatoes and Tomato Paste
Stir in the sun-dried tomatoes and tomato paste.
Cook, stirring constantly, until the tomato paste deepens in color, about 2 minutes.
Add Broth and Seasonings
Pour in chicken broth and heavy cream.
Add basil, kosher salt, Italian seasoning, garlic powder, and crushed red pepper.
Bring the mixture to a boil over medium heat, stirring occasionally, about 12 minutes.
Cook the Pasta
Add the uncooked pasta shells and reduce the heat to medium-low.
Cook, stirring occasionally, until the pasta is al dente, about 12 minutes.
Finish the Soup
Reduce the heat to low and stir in spinach, shredded chicken, cream cheese, and Parmesan cheese.
Cook, stirring frequently, until the cheeses are melted and the chicken is heated for about 5 minutes.
Garnish and Serve
Ladle the soup into bowls. Garnish with additional Parmesan, fresh basil, and a sprinkle of crushed red pepper, if desired.
Serve immediately while warm and creamy.