Mix the sauce ingredients in a bowl and set aside.
Heat the oil in a skillet or wok over medium high heat. While the oil is heating up, stir and mix the egg into the chicken bowl. Add the cornstarch and continue mixing until the chicken is coated and there is very little dry cornstarch left.
Spread the chicken pieces out evenly and fry for about 2 minutes or until browned and crispy on the bottom side. Flip the chicken to brown the other side and fry for another 2 minutes or until browned and crispy on the bottom side. Depending on how big your skillet or wok is, you may need to shallow fry the chicken in batches.
Transfer the chicken to a paper towel lined plate (to soak up extra grease). Drain all but 1 tbsp of oil in the skillet.
Over medium high heat, stir fry the garlic, white portions of the scallions, and ginger, if using, for 30 seconds. Stir the sauce mixture for a few seconds to dissolve the cornstarch again and then pour it into the pan. Let it simmer and thicken for 30 seconds to a minute. Add in the chicken and the green portions of the scallions and mix.