In a wok or large skillet over high heat, stir-fry the bell peppers and garlic in the oil for about 3 minutes. Add the bok choy, carrot, onion and water chestnuts. Continue stir-frying until the bok choy is tender. Remove from the heat. Add the bean sprouts, soy sauce, vinegar and ginger. Toss well. Adjust the seasoning.