Heat the oil and sauté the onion until browned. Add the ginger and continue to sauté for a couple of minutes. Mix the curry powder and turmeric with enough water to make a wet paste, and add it to the onion mixture. Sauté for an additional 3 to 4 minutes. Add the chiles, tomato, chicken, and potatoes, season with salt and cook for 5 minutes. Set aside to cool.