Heat olive oil in a large stockpot or Dutch oven over medium heat. Add Italian sausage to the skillet and cook until browned, about 3-5 minutes, making sure to crumble the sausage as it cooks; drain excess fat. Stir in garlic and onion. Cook, stirring occasionally, until tender, about 3-4 minutes.

Whisk in chicken stock, crushed tomatoes, basil, oregano, red pepper flakes and 1 cup water; season with salt and pepper, to taste. Bring to a boil and stir in tortellini; reduce heat and simmer until tortellini is cooked through, about 5-6 minutes.

Stir in heavy cream and Parmesan until well combined and heated through, about 2-3 minutes.

Serve immediately, garnished with croutons, if desired.