Pound chicken breasts with a mallet to an even thickness and season both sides with sugar, salt, and garlic powder. Grill chicken 4-6 minutes on each side or until no longer pink inside. Remove from grill and cut into bite-sized strips. Set aside.
In a bowl combine sugar, soy sauce, lemon juice, garlic, and ginger. Pour into a wok or saucepan. Heat the mixture until almost at a boil. Combine cornstarch and water. Once the sauce starts to boil add the cornstarch mixture and stir until thickened.
Add grilled chicken to the wok and coat with the sauce. Simmer until heated thoroughly.