Coat the chicken cubes with cornstarch.
In a bowl, mix the egg, flour, baking powder, and salt.
Add the chicken and coat well with the mixture.
In a large non-stick skillet, heat the oil over high heat.
Add the chicken and cook for 10 minutes, stirring often, until the chicken is golden brown on the outside and no longer pink on the inside.
Place the chicken on a plate. Set aside.
Add the sesame oil, ginger, and green onions to the skillet.
Cook over medium-high heat for 3 minutes. Add the water, rice vinegar, and sugar.
Simmer until the sugar is completely dissolved.

Meanwhile, mix the cornstarch with the soy sauce.
Add the soy sauce mixture, oyster sauce, and ketchup to the skillet.
Simmer for 2 minutes or until the sauce thickens.
Return the chicken to the sauce and stir to reheat the chicken.
Serve on a bed of rice and garnish with sliced green onions.