Step 1Place the chicken in a large stew pan or pot. Sprinkle with salt and pepper to taste and the cumin and turmeric. Add the onion, carrots, garlic and water. Bring to a boil. Cover and cook over low heat, skimming the foam occasionally, 1 hour.
Step 2Peel the potatoes, if desired. Halve them (or quarter if large), add to the soup and simmer 10 minutes. Add the zucchini, green beans and corn, if using, and bring to a simmer. Cover and cook the soup over low heat until the vegetables are tender, 15 minutes. Skim off the fat. (If you're making the soup ahead, refrigerate, then skim off the fat). Season generously with salt and pepper. Remove the onion if whole and then the chicken, discarding any remaining skin, and cut the meat from the bones. Discard the bones and return the meat to soup. Serve the soup in fairly shallow bowls with the chicken and vegetables.