1. Cut lamb into thin slices and then cut in bite-sized pieces. Mix lamb with five-spice powder, garlic, soy sauce, and sherry; cover and refrigerate 1 to 4 hours. Drain meat, reserving marinade.

2. Heat oil in a large heavy frying pan or wok. In it cook lamb, about half at a time, turning and stirring until it is just browned. Remove pan from heat; return all the cooked lamb to the pan. Blend corn starch and water into reserved marinade; add to meat.

3. Return to heat and cook. Stirring until sauce is thickened. Stir in green onions. Serve immediately.