Mix the sliced chicken with 1 tablespoon of oil, until the pieces are evenly coated. Dredge all of the chicken in the cornstarch, shaking off the excess until the chicken is just lightly coated.
Heat ⅓ cup oil in a wok over high heat. At this point, if the chicken has absorbed the cornstarch and gets moist again, dredge the pieces again before frying. Just before the oil starts to smoke, spread the chicken pieces evenly in the wok, and fry for 1 minute, or until browned and crispy.
Turn the chicken, and let the other side fry for another 30 seconds or until browned and crispy. Transfer to a sheet pan or plate lined with paper towels. The chicken should be fried on all sides with a crusty coating.
Drain the oil from the wok, leaving 1 tablespoon behind, and set over medium high heat. Add the ginger fry for 20 seconds, until fragrant. Add the dried chili peppers, if using, the garlic, and the white portions of the scallions. Stir fry for another 15 seconds, and add the soy sauce, brown sugar, and chicken stock (or water). Bring the sauce to a simmer, and stir constantly until the brown sugar is completely dissolved.
Let the sauce simmer for another 2 minutes, and slowly stir in the cornstarch-water mixture until the sauce coats the back of a spoon. Add the chicken and the green portions of the scallions. Toss everything together for another 10 seconds.
There should be almost no liquid--the sauce should cling to the chicken. If you still have excess sauce, add more of the cornstarch slurry, and increase the heat slightly. Stir until thickened.