In a large Dutch oven, cook Italian sausage over medium-high heat, breaking it into crumbles. Drain excess grease if necessary.
Add onion and cook for 3-4 minutes until softened. Stir in garlic, tomato paste, sun-dried tomatoes, oil from sundried tomatoes, Italian seasoning, and red pepper flakes. Cook for another minute.
Pour in chicken broth and bring to a gentle boil. Reduce heat and simmer for 8-10 minutes.
Stir in heavy cream and bring back to a gentle simmer.
Add refrigerated tortellini and cook according to package directions, usually 3-5 minutes.
Stir in spinach and Parmesan until the spinach wilts and cheese melts. Taste and adjust salt and pepper.