1. Heat the oven to 400 degrees F. Place a 2-quart clay pot or heavy casserole with a cover in the oven to heat.
2. Trim any fat from the chicken and cut the chicken into 1-inch cubes. Combine the salt, pepper, ginger and cornstarch in a bowl. Toss the chicken with the cornstarch mixture and set aside.
3. Bring 2 cups water to a boil in saucepan over high heat. Add the potatoes and carrot; cover and cook 2 minutes. Drain and set aside.
4. Heat a heavy nonstick skillet or wok over high heat until hot. Add the vegetable oil and the chicken; stir and cook until lightly browned, about 1 minute. Add the garlic, onion, curry powder and tomato and stir-fry 1 minute. Add the potatoes, carrot, soy sauce and sugar and continue to stir until well mixed. Turn off the heat and transfer the mixture to the heated clay pot. Cover the clay pot and return to the oven for 15 to 20 minutes. Serve hot.
5. To hold the finished dish, turn the oven off and keep warm until ready to serve. Stir in the scallion just before serving.