Heat the olive oil in a large pot over medium heat.
Add the diced onion and sauté until translucent, about 5 minutes.
Stir in the minced garlic and cook for an additional minute.
Add the sliced carrots and celery, stirring to combine.
Pour in the broth and add the diced tomatoes along with their juice.
Bring the mixture to a boil, then reduce to a simmer.
Stir in the tortellini and cook according to package instructions, typically 3-5 minutes.
Add the spinach or kale and stir until wilted, about 1-2 minutes.
Season the soup with oregano, salt, and pepper to taste.
Serve hot, garnished with fresh herbs or grated cheese if desired.