In a blender, combine ginger, garlic and 2 teaspoons of water to make a paste. Heat 2 teaspoons of oil in a skillet. Stir fry chicken until lightly browned and set aside. Wipe out the pan and heat remaining 2 teaspoons of oil, cook onion for 2 minutes. Add 2 tablespoons of water, reduce heat and cook stirring ocassionally, about 20 minutes. Add tomato and ginger paste. Cook, mashing tomatoes with spoon, add green chiles and chicken and 1/2 cup of water. Bring to a boil. Reduce heat and simmer for 5 minutes. Add black pepper and cilantro. Continue cooking until chicken is cooked. Salt to taste. Let stand 5 minutes and serve.