In a large pot, heat the olive oil over medium heat. Add the diced onion and sauté for about 5 minutes until translucent.
Stir in the minced garlic, carrots, and celery. Cook for an additional 5 minutes until the vegetables begin to soften.
Add the dried oregano, dried basil, and red pepper flakes (if using). Stir to combine and cook for 1 minute until fragrant.
Pour in the diced tomatoes with their juices and the vegetable broth. Bring the mixture to a boil.
Add the rinsed quinoa to the pot. Reduce the heat to low, cover, and simmer for about 15 minutes, or until the quinoa is cooked and the vegetables are tender.
Stir in the cannellini beans and chopped spinach. Cook for an additional 5 minutes until the spinach is wilted.
Season with salt and pepper to taste. Serve hot, garnished with fresh parsley and grated Parmesan cheese if desired.