In a small mixing bowl, whisk together the chicken stock, soy sauce, sherry, cornstarch, and sugar until the cornstarch is dissolved. Set this aside.
Heat your wok or heavy-bottomed skillet over high heat. Add half the oil and the chicken strips. Sauté the chicken until it is opaque (white), stirring often, approximately 3 to 5 minutes. Using a slotted spoon, remove the chicken to a bowl.
Add the rest of the oil to the pan along with the garlic, ginger, onions, mushrooms, and celery. Cook for a couple of minutes until the garlic and ginger are fragrant.
Add the bell pepper and continue to cook for another minute.
Give the sauce another good stir. Over high heat, stir in the chicken, snow peas, and broth mixture. Allow this to come to a full boil. Cook just until the sauce reduces and clings to the chicken and vegetables, not more than 30 seconds to 1 minute.
Serve immediately over steamed or boiled rice.