Heat the olive oil in a large pot or Dutch oven over medium heat. Add the chopped onion and cook until softened, about 5 minutes.
Add the minced garlic and cook for 1 minute until fragrant.
Pour in the diced tomatoes (with juice), vegetable broth, Italian seasoning, salt, and pepper. Bring the mixture to a simmer.
Add the refrigerated tortellini to the simmering liquid. Cook according to package directions, usually about 8 to 10 minutes, stirring occasionally to prevent sticking.
Stir in the fresh spinach until it wilts completely into the sauce, about 2 minutes.
Reduce the heat to low. Stir in the heavy cream and grated Parmesan cheese until the sauce is smooth and creamy.
Serve immediately.
Notes
If you prefer a thicker sauce, allow the mixture to simmer uncovered for an extra 3 to 5 minutes before adding the cream.
Use frozen tortellini if fresh is unavailable; adjust cooking time as needed.
For a richer flavor, substitute half the vegetable broth with chicken broth.