In a medium bowl, whisk together orange zest, orange juice, water, Shaoxing wine, rice vinegar, soy sauce, oyster sauce, sugar, grated garlic, grated ginger, and red pepper flakes if using. Set sauce aside.
In a large bowl, combine chicken cubes with Shaoxing wine, sesame oil, water, and eggs. Mix well to coat all pieces.
Add flour, cornstarch, salt, and white pepper to the chicken mixture. Stir until a thick, wet batter forms and all chicken pieces are evenly coated.
Heat cooking oil to 350°F in a large pot or deep fryer. Working in batches, carefully fry chicken pieces until golden brown and crispy, about 4-5 minutes per batch.
Remove chicken and drain briefly on paper towels. Immediately toss the hot, crispy chicken in the prepared orange sauce until well coated. Serve immediately.