Heat olive oil in a large pot over medium heat.
Add the Italian turkey sausage, breaking it up with a spoon, and cook until browned and cooked through, about 6-8 minutes.
Add the diced onion, garlic, carrots, celery, and red bell pepper to the pot. Cook, stirring occasionally, until the vegetables are softened, about 5 minutes.
Stir in the dried Italian seasoning, crushed red pepper flakes, salt, and black pepper. Cook for 1 minute until fragrant.
Pour in the chicken broth and diced tomatoes with their juice. Stir to combine and bring the mixture to a boil.
Add the small pasta shells to the pot. Reduce heat to a simmer and cook until the pasta is tender, about 10 minutes.
Stir in the chopped baby spinach and cook until wilted, about 2 minutes.
Reduce heat to low and stir in the heavy cream and grated Parmesan cheese until the cheese is melted and the soup is creamy.
Taste and adjust seasoning with additional salt and pepper if needed.
Serve hot, garnished with extra Parmesan cheese if desired.