In a medium bowl combine ½ cup cornstarch, flour, salt and pepper. Add in the egg, 1 tablespoon oil, and water. Whisk until smooth. Add the chicken cubes to the mixture and mix well.

Heat oil in a deep-fryer or large saucepan and heat to 350 degrees Add the chicken cubes in batches and deep-fry for 3-5 minutes or until golden brown and fully cooked (the internal temperature has reached 165 degrees F.).

Drain on a plate lined with paper towels.

Add 1 tablespoon of oil to a large skillet or wok and heat to medium-high heat. Add in orange juice, soy sauce, vinegar, brown sugar, garlic and orange zest. Mix 2 tablespoons cornstarch and 2 tablespoons water in a separate bowl. Then add to the sauce in the pan. Stir until smooth and thick, about 3-4 minutes.

Mix the fried chicken pieces with the sauce. Top with sesame seeds and green onions if desired. Serve immediately.