In a large pot, heat the olive oil over medium heat. Add the diced onion and sauté for about 5 minutes until the onion is translucent.
Stir in the minced garlic and dried oregano, cooking for an additional 1-2 minutes until fragrant.
Pour in the vegetable broth and canned tomatoes with their juices. Bring the mixture to a gentle simmer.
Add the tortellini to the pot, cooking according to package instructions, typically around 5-7 minutes until they are floating and tender.
Once the tortellini are cooked, stir in the chopped basil, balsamic vinegar, salt, and black pepper. Simmer for 2-3 more minutes to let the flavors meld.
Serve hot, garnished with grated Parmesan cheese on top.