For the chicken: In a large bowl, sprinkle the chicken with salt and pepper. Add the cornstarch and toss to coat. For the sauce: In another smaller bowl, combine the stock, cornstarch, oyster sauce, soy sauce and chili sauce. Mix well and set aside. For the stir-fry: Heat a wok over high heat and, when the wok starts to smoke, add the peanut oil. Add the ginger and stir-fry for a few seconds. Then add the chicken, let settle for 1 minute, and then stir-fry for 3 minutes more. As the chicken starts to turn opaque, add the rice wine and stir-fry for 30 seconds. Stir in the reserved sauce and bring to a boil. Add the mushrooms and bok choy stalks and cook for 1 minute. Then stir in the bok choy leaves and cook for another minute. Remove from the heat and stir in half the scallions. Transfer to a serving dish, garnish with the remaining scallions and serve immediately.