Heat olive oil in a large pot over medium heat. Add onion and cook until softened, about 5 minutes. Add garlic and cook for 1 minute more.
Stir in crushed tomatoes, vegetable broth, basil, oregano, and red pepper flakes (if using). Bring to a simmer.
Add tortellini and cook according to package directions, about 3-5 minutes for fresh and 6-8 minutes for frozen.
Stir in heavy cream and heat through. Do not boil.
Serve immediately, garnished with Parmesan cheese.
Notes
For a thicker soup, you can add a slurry of cornstarch and water (1 tablespoon cornstarch mixed with 2 tablespoons cold water) to the soup while it is simmering.