In a small bowl, combine cornstarch, vinegar, sugar and soy sauce and mix together.
Preheat work over high heat. When wok begins smoking, reduce heat to medium-medium-high and add garlic and ginger. Stir-fry until fragrant, then push seasonings up the side of the wok, turn heat to high, and wait for 1 minute to heat.
Brown chicken seasoned oil in hot wok.
Add water chestnuts and onion to wok and stir-fry for one minute.
Add celery and carrot to wok and stir-fry for 45 seconds.
Add green bell pepper to wok and stir fry for 1 to 2 minutes.
Pour sauce into the wok, along with the pineapple. Stir together and bring to a full boil. Serve immediately over cooked rice.