Heat olive oil in a large pot or Dutch oven over medium heat. Add the chopped onion and cook until softened, about 5-7 minutes.
Add the minced garlic and cook for 1 minute more until fragrant.
Pour in the crushed tomatoes, vegetable broth, dried basil, dried oregano, and red pepper flakes (if using). Stir to combine.
Bring the soup to a simmer, then reduce heat and let it cook for 10 minutes to allow the flavors to meld.
Add the refrigerated tortellini to the pot and cook according to package directions, usually about 5-7 minutes, until tender.
Stir in the heavy cream and grated Parmesan cheese. Heat through gently, but do not boil.
Season with salt and black pepper to taste.
Ladle the soup into bowls and garnish with fresh basil leaves before serving.
Notes
For a dairy-free option, substitute the heavy cream with full-fat coconut milk or a dairy-free creamer. Use nutritional yeast instead of Parmesan cheese.
Leftovers can be stored in an airtight container in the refrigerator for up to 3 days. The tortellini may absorb more liquid, so you may need to add a splash of broth or water when reheating.
You can add other vegetables like spinach or chopped carrots along with the onion.