For sauce, in a small bowl stir together water, hoisin sauce, soy sauce, sherry, and cornstarch. Set aside.
Pour cooking oil into a wok or large skillet. (Add more oil as necessary during cooking.) Preheat over medium-high heat. Stir-fry ginger and garlic in hot oil for 15 seconds. Add zucchini and onion; stir-fry for 3 to 4 minutes or until zucchini is crisp-tender. Remove zucchini mixture from the wok.
Add mushrooms and sweet pepper strips to the hot wok; stir-fry about 2 minutes or until crisp-tender. Return zucchini mixture to the wok. Push vegetables from the center of the wok.
Stir sauce. Add sauce to the center of the wok. Cook and stir until thickened and bubbly. Stir all ingredients together to coat with sauce. Serve immediately. Makes 6 side-dish servings.