In a large stockpot, combine the chicken broth, potatoes, onions, carrots, and celery. Bring to a boil, reduce heat to medium-high, and simmer until the potatoes are tender, about 30 minutes.

Add zucchini, tomato sauce, garlic, parsley, and cilantro. Reduce heat to medium-low and cook for 10 to 15 minutes more, or until the zucchini is just tender. Season to taste with black pepper and serve.