Toss chicken pieces with 1/2 cup cornstarch in a bowl until evenly coated.
Heat vegetable oil in a large skillet over medium-high heat and cook chicken in batches until golden brown and crispy, about 3-4 minutes per side, then transfer to a plate.
In the same skillet, add garlic and ginger, cooking for 30 seconds until fragrant, then add orange juice, soy sauce, honey, rice vinegar, and orange zest.
Bring sauce to a simmer, add the cornstarch slurry, and cook for 2-3 minutes until sauce thickens.
Return chicken to the skillet, toss to coat in the sauce, drizzle with sesame oil, and cook for another 2 minutes until chicken is fully coated and heated through.
Serve immediately over rice, garnished with green onions or sesame seeds if desired.