In a large stock pot, heat the oil on medium heat then add the onion, carrot, and celery and cook until softened, about 10 minutes.
Add the tomatoes and cook a couple minutes to concentrate the tomato juices. Then add the chicken stock, water, salt, oregano, zucchini, green beans and potato. Cover and simmer for 20 minutes until potatoes are fork tender. If you want to add the meatballs, do so after you bring the soup to a boil and before you start the 20 minutes simmer.