In a saucepan, heat oil and saute onions, celery, cinnamon and peppercorns until onions and celery are soft. Do not let onions brown.
Add chicken, garlic, ginger, salt, turmeric and tomatoes. Mix well, cover and cook for 15 minutes. Stir occasionally.
Add 6 cups of water, potatoes and cilantro. Mix well, cover and cook for 15 minutes or until the potatoes are done.
Add lemon juice, mix and serve.
Note: Discard whole spices while eating.