Combine first 3 ingredients in a small bowl, stirring until cornstarch dissolves. Stir in sherry and next 5 ingredients. Set aside.
Snap off tough ends of asparagus. Remove scales from stalks with a knife or vegetable peeler, if desired. Cut asparagus diagonally into 2-inch pieces.
Coat a wok with cooking spray; drizzle 1 teaspoon vegetable oil around top of wok, coating sides. Heat at medium-high (375°) until hot. Add gingerroot and garlic; stir-fry 10 seconds. Add asparagus; stir-fry 2 minutes. Add 2 tablespoons water, cooking until water evaporates. Add red pepper and water chestnuts; stir-fry 1 minute.
Add chicken broth mixture and green onions to wok; cook, stirring constantly, 1 minute or until mixture is thickened. Serve immediately.