Whisk together orange juice, soy sauce, sugar, rice vinegar, ginger, garlic, and orange zest in a small bowl until sugar dissolves.
Toss chicken pieces with cornstarch until evenly coated.
Heat vegetable oil in a large skillet over medium-high heat and fry chicken in batches for 6 to 8 minutes, turning once, until golden and cooked to 165°F / 74°C.
Pour the orange sauce into the same skillet and simmer for 2 to 3 minutes until thickened and glossy.
Return the crispy chicken to the skillet and toss until every piece is coated with the sticky orange sauce.