Slice sausage into 1/4 pieces. Cut onions into thin wedges. In a small bowl stir together water, sherry, soy sauce, cornstarch, garlic powder, and pepper; set aside.
Preheat wok or skillet over high heat; add oil. Add onions and stir fry 3 minutes. Add cauliflower and stir fry 3 minutes more. Transfer vegetables to a bowl. Add sausage to wok and cook 2 minutes. Punch to the sides. Stir cornstarch mixture, then add to the center of the wok or skillet. Cook and stir until thick and bubbly. Stir in vegetables. Cover and cook 1 minute more. Serve over noodles.