In a large pot, heat the olive oil over medium heat. Sauté the onion and garlic, stirring frequently until onions are soft, about 5 to 7 minutes. Add broth and the tomatoes and increase the heat to high, bringing the soup to a boil. Add the tortellini and cook according to package instructions. When tortellini is almost done, add spinach and taste. Season with salt and pepper. Serve with Parmesan on top.