In a 3-quart soup pot, heat olive oil over medium high heat. Saute the onion and garlic, stirring often until onions are translucent, about 5 to 7 minutes. Add broth and tomatoes, turn heat up to high, and bring to a boil. Add the tortellini and cook according to package instructions. When tortellini is almost done, add spinach and taste, adjusting seasonings with salt and pepper. Serve immediately. Garnish each serving with a sprinkling of Parmesan.