In a shallow bowl. whisk together cornstarch, flour, salt, garlic, onion powder, Chinese 5 spice and pepper OR red pepper flakes. Place beaten eggs with water into a separate dish.
Sprinkle 2 tablespoons seasoned dry ingredients over chicken, toss to coat. Next, dip chicken in egg then back into the dry ingredients.
Heat 1 inch oil in large skillet over medium-high heat. Cook chicken pieces in batches for 2-3 minutes, turning for even browning. Remove to a platter using a slotted spoon, keep warm. (You can also deep fry at 350°F)
Meanwhile, in a small saucepan over medium heat cook rice wine vinegar, pineapple juice, ketchup, soy sauce, apple cider vinegar, granulated sugar, brown sugar, garlic and salt. Cook stirring until sugar has dissolved, then lower the heat and let simmer while you make the chicken. At the end of cooking, dissolve cornstarch in a small amount of cold water, whisk into the sauce to thicken. Repeat, if desired.
Pour sauce over cooked chicken and toss to coat. Start with half sauce and serve the remaining on the side.
Serve immediately over rice garnished with green onion and sesame seeds, if desired.