In a large pot, heat olive oil over medium heat. Add chopped onion and sauté until translucent, about 5 minutes.

Add minced garlic, cumin, and oregano, and cook for another minute until fragrant.

Stir in diced tomatoes with their juice and salsa if using. Cook for 3 minutes to let the flavors meld.

Add black beans, white beans, and vegetable broth. Bring the mixture to a boil.

Reduce heat to a simmer and stir in the quinoa. Cover and cook for 20 minutes, or until quinoa is cooked and the soup has thickened.

Season with salt and pepper to taste. Serve hot, garnished with chopped cilantro and slices of avocado.