In a medium bowl, combine 1 and 1/2 tablespoons of cornstarch, water, sugar, soy sauce, vinegar and hoisin sauce.
Whisk until blended. set aside.
Toss chicken in remaining cornstarch and set aside.
Add oil to a skillet and heat over medium high heat.
Cook chicken pieces in small batches until all are browned.
After removing last chicken from pan, drain all but about a tablespoon of the oil.
Add ginger, pepper flakes and garlic.
Heat over medium heat until garlic is fragrant.
Add back cooked chicken and toss to coat.
Add sauce mixture and stir until heated and sauce has thickened (1-2 minutes).
Optionally, garnish with sliced green onions and serve over rice.