Make the orange sauce. In a medium mixing bowl, add the orange juice, orange zest, soy sauce, oyster sauce, white vinegar, and brown sugar. Mix until combined and set aside.

Prepare the chicken. In a large mixing bowl, add the chicken, salt, white pepper, and egg, and mix until combined. Then toss each chicken with cornstarch until evenly coated. Set aside.

Fry the chicken. Heat about 1 ½ inches of vegetable oil in a wok or heavy-bottomed pot over medium-high heat until it reaches 365°F (185°C). Gently place the battered chicken in the oil with a spider strainer. Work in 3 batches to prevent overcrowding the pan. Fry for about 6-7 minutes, flipping halfway until golden brown. Remove the chicken with a spider strainer and place it on a wire rack to drain excess oil.

Double Fry (optional). For a crispier chicken, increase the heat to 385°F (196°C) and work in batches to fry the chicken for 2 minutes or until golden brown and crispy. Remove the chicken and place it on a wire rack to drain excess oil. Be sure to increase the oil to 385°F (196°C) before frying the second batch.

Cook the sauce. Heat one tablespoon of oil in a large pan over medium heat. Add the garlic, ginger, and chili flakes if using. Saute for 20 seconds until fragrant. Then add the orange sauce and bring to a simmer, stirring continuously for about 2-3 minutes. Once the sauce begins to simmer, mix the cornstarch slurry, and slowly mix it into the sauce until it thickens.

Add chicken and green onion. When the sauce has thickened, turn off the heat, add the chicken and green onions. Toss to combine.

Serve. Serve immediately with steamed rice and enjoy!