In a large pot, heat a small amount of oil over medium heat. Add the diced onion, celery, and red pepper, and sauté for about 5 minutes, until the vegetables begin to soften.
Stir in the carrots, zucchini, and baby potatoes, and cook for another 3-4 minutes. Add the diced tomatoes, mushrooms, spinach, and green beans to the pot.
Pour in the vegetable broth, making sure all the vegetables are submerged. Stir in the dried thyme, red chili flakes, salt, and pepper.
Bring the soup to a boil, then reduce the heat and let it simmer for 20-25 minutes, or until the vegetables are tender.