Marinate chicken cubes with scallion, ginger, salt, pepper, soy sauce, oyster sauce, and egg. Mix well.
In a separate bowl, mix cornstarch, baking powder, and wheat flour.
Coat marinated chicken evenly with the flour mixture.
Shake off excess flour, dip chicken in water, and coat with flour mixture again.
Heat oil to 180°C (350°F) and deep fry chicken on low heat until golden brown.
Drain on paper towels and serve hot. Enjoy!