Whisk together orange juice, soy sauce, sugar, rice vinegar, ginger, garlic, and orange zest in a small bowl until the sugar dissolves, then set aside.
Toss the chicken pieces with cornstarch until evenly coated, shaking off any excess.
Heat vegetable oil in a large skillet over medium-high heat, then fry the chicken in batches for 6 to 8 minutes, turning occasionally, until golden and crispy and the internal temperature reaches 165°F / 74°C.
Remove the chicken to a plate, pour the orange sauce into the same skillet, and simmer for 3 to 4 minutes until thickened and glossy.
Return the chicken to the skillet and toss quickly in the sauce for 30 seconds to coat evenly.
Serve immediately to keep the coating crisp.