In a medium bowl, add the sliced chicken breast, 1 teaspoon soy sauce, 2 teaspoons cornstarch and 1 tablespoon vegetable oil. Mix well. Heat your wok over high heat until smoking. Add 2 tablespoons vegetable oil, and sear the chicken until it just turns opaque (it can still be slightly pink). Remove the chicken from the wok and set aside.
Reduce the heat to medium, and add another couple tablespoons of oil to the wok. Add the ginger and cook for 1 minute. Add the garlic, sha cha sauce, and sugar, and fry this mixture for 2 minutes.
Then add the chicken back to the wok along with the scallions and the remaining tablespoon of soy sauce. Increase the heat to high, and stir-fry for 1 minute, until the scallions are wilted. Serve immediately with steamed rice!