In a bowl, mix together the egg, salt, and pepper, and 2 tablespoons cornstarch. Add the chicken cubes, mix to coat, and marinate for at least 15 minutes. In a small bowl, combine the sauce ingredients and reserve.
Heat a wok over high heat. Add oil and heat to 350 degrees Fahrenheit. With tongs, remove the chicken cubes individually, dust with 1 tablespoon cornstarch, and place in the oil. Deep-fry for 1 1/2 to 2 minutes, until the chicken is browned and crisp. Turn off the heat. Remove the chicken with a Chinese strainer and drain over a bowl. Pour off all but 1 1/2 tablespoons of the oil from the wok.
Heat the wok over high heat for 20 seconds. When a wisp of white smoke appears, add the chilies and stir for 15 seconds. Add the scallion and stir for 30 seconds. Add the chicken and cook, stirring, for 1 minute. Stir the sauce mixture, pour into the wok, stir well, and cook until the chicken cubes are completely coated with sauce, about 1 1/2 minutes. Turn off the heat, transfer to a heated dish, and serve.