In a medium bowl, whisk together cornstarch and flour. In another bowl, whisk together egg and water.

Dip each chicken piece into the egg mixture, then dredge in the cornstarch mixture, ensuring it's fully coated.

Heat vegetable oil in a large skillet or Dutch oven to 350°F (175°C).

Carefully add chicken pieces to the hot oil in batches and fry for 3-4 minutes per side, or until golden brown and cooked through. Remove and place on a wire rack to drain excess oil.

In a small saucepan, combine orange juice, rice vinegar, soy sauce, sugar, ginger, garlic, and red pepper flakes (if using). Bring to a simmer.

Stir in the cornstarch slurry and cook, stirring constantly, until the sauce thickens.

Add the fried chicken to the saucepan with the orange sauce and toss to coat evenly.

Serve immediately with rice and steamed vegetables, if desired.