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 and cook for an additional 1 minute.
Add the carrots, celery, zucchini, mushrooms, and green beans to the pot. Sauté the vegetables for about 5-7 minutes until they start to soften.
Pour in the vegetable broth and diced tomatoes. Stir in the dried thyme, dried oregano, salt, and pepper. Bring the mixture to a boil.
Once boiling, add the rinsed quinoa. Reduce the heat to low, cover the pot, and let it simmer for 15-20 minutes, or until the quinoa is cooked and the vegetables are tender.
Stir in the fresh spinach and lemon juice. Cook for an additional 2-3 minutes until the spinach is wilted. Adjust seasoning if needed.
Serve hot, garnished with fresh herbs if desired.