Heat oil over medium-high heat in a large saucepan. When oil is hot, add onion, carrots, celery, red pepper, garlic cloves and cabbage. Stir to coat and saute for about 2-3 minutes, until veggies are softened but not browned.
Add quinoa and stir until mixed in with the vegetables. Saute for another 2 minutes.
Add tomatoes and broth and simmer on low-medium heat for about 20-30 minutes or until veggies are cooked to your liking. The longer you cook it, the more the quinoa will naturally thicken the soup.
When soup is done, stir in fresh basil and add salt and pepper to taste.