Bring broth to a boiling medium sauce pan.Combine cornstarch and water in a small bowl.Set aside.Heat oil in wok over high heat.Add beef.Stir fry until no longer pink, breaking larger pieces with a wooden spoon.Add garlic and Chinese cabbage.Stir fry about 1 minute.Reduce heat and add broth mixture;stir until thickened.Add tofu;gently stir until heated, about 1 minute.Spoon tofu mixture over rice and garnish with green onions.Serves 4.