Wash and chop all your vegetables: dice the onion, mince the garlic, slice the carrots and celery, cut the zucchini and bell pepper into bite-sized pieces, and trim the green beans.
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 minute.
Add the sliced carrots and celery, cooking for another 5 minutes. Then, add the diced zucchini, bell pepper, and green beans. Stir to combine. Pour in the canned diced tomatoes with their juices and the vegetable broth.
Add the dried thyme, dried basil, salt, and pepper. Bring to a boil, then reduce heat to low and let it simmer for about 20 minutes.
After 20 minutes, check the vegetables for tenderness. Stir in the fresh spinach and lemon juice, cooking for an additional 2-3 minutes until the spinach wilts. Adjust seasoning if needed and serve hot.