Whisk together orange juice, soy sauce, sugar, rice vinegar, ginger, garlic, and orange zest in a small bowl and set aside.
Toss chicken pieces in cornstarch until evenly coated.
Heat vegetable oil in a large skillet over medium-high heat and fry chicken in batches for 3 to 4 minutes per side 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 in the sticky orange sauce.
Serve immediately over steamed rice with sesame seeds or green onions if desired.