In a large pot over medium heat, heat olive oil and cook diced onion until softened.
Add Italian sausage and cook until browned. Drain excess grease if needed.
Stir in minced garlic, tomato paste, Italian seasoning, and red pepper flakes. Cook for 1–2 minutes.
Pour in chicken broth and diced tomatoes. Bring to a boil.
Stir in heavy cream and cheese tortellini. Reduce heat and simmer for 8–10 minutes, or until tortellini are tender.
Add baby spinach and cook until wilted. Season with salt and pepper to taste.
Serve hot, garnished with grated parmesan if desired.