1. Heat the oil in a 4-6qt saucepan over medium high heat. Add the onions and cook, stirring, until softened, about 5 minutes. Add the garlic and cook, stirring, until the onions are translucent and the garlic is softened, another 3 minutes. Add the carrot, celery, oregano, thyme, and red pepper flakes. Cook, stirring, until softened, 5-6 minutes.
2. Add the tomatoes with their juices and the broth and bring to a boil. Reduce the heat and simmer for 10-15 minutes. Add the spinach and tortellini. Cook 6 minutes.