In a large Dutch oven over medium-high heat, brown the Italian sausage, breaking it into small crumbles, until no longer pink.
Drain all but 1 tablespoon of fat from the pot. Add the onion and sauté for 5 minutes until translucent.
Stir in the garlic, sun-dried tomatoes, oregano, and red pepper flakes; cook for 60 seconds until fragrant.
Add the chicken broth and bring to a rolling boil.
Reduce heat to medium and add the refrigerated tortellini. Simmer for 3 to 5 minutes, or until the tortellini are al dente.
Lower heat to medium-low and stir in the baby spinach, allowing it to wilt for approximately 1 minute.
Pour in the heavy cream and grated Parmesan cheese, stirring constantly until the cheese is melted and the soup is well combined.
If a thicker consistency is desired, stir in the cornstarch slurry and simmer for an additional 2 minutes.
Taste and adjust seasoning with salt and black pepper before serving.