In a mixing bowl, combine the flour, cornstarch, salt, chicken powder, and white pepper. Add the water, eggs and 2 tablespoons of cooking oil. Mix until you have a smooth batter. Add the chicken breast pieces to the batter, ensuring they are fully coated. Cover the bowl and chill the marinated chicken in the fridge for 30 minutes.
Heat enough cooking oil in a deep pan or wok over medium heat for frying. Once the oil is hot, carefully add the marinated chicken pieces in batches, frying until golden brown and crispy, about 4-5 minutes per batch. Remove the fried chicken and drain on paper towels to remove excess oil.
In a separate pan, heat 1 tablespoon of cooking oil over medium heat. Add the chili flakes, minced ginger, and garlic. Sauté until fragrant.
Add the white sugar, brown sugar, orange juice, vinegar, and soy sauce. Stir well and bring to a simmer.
Slowly stir in the cornstarch slurry, continuously stirring until the sauce thickens. Once the sauce has thickened to your desired consistency, turn off the heat.
Add the fried chicken to the sauce, tossing to coat each piece evenly. Pour in the sesame oil to give more flavor to the sauce.
Serve the Orange Chicken hot, garnished with sesame seeds or green onions if desired.