If using shrimp, clean and devein. Saute them lightly on both sides until they become pinkish, then set aside. If using chicken, cut the meat into 1" strips and set aside. In a saucepan or wok, heat the oil and "splutter fry" the curry powder and red chili powder and then the garlic rapidly for 30 seconds. Add the tomatoes, then add the ginger, if desired, and salt; mix well and bring to a boil. Add the chicken or shrimp, and simmer until cooked (3-5 minutes for the shrimp, 6-10 minutes for the chicken). Finally, do the "fimmering" process, simmering on high heat until the oil floats to the top for a minute or so. Remember that overcooking or overspicing can kill the curry. Use the optional cream to tame the curry or adjust the flavor. Garnish with freshly chopped coriander and a squeeze of lemon juice. Serves 2 as a main dish, 3-4 when served with other dishes.