First, prepare the sauce: In a medium bowl, whisk together the orange juice, zest, soy sauce, vinegar, brown sugar, cornstarch, garlic, ginger, and red chili flakes. Set aside.

Prepare the chicken: In a small, shallow bowl, whisk together the cornstarch, salt, and pepper. Dredge the cubed chicken pieces in the cornstarch mixture and coat each piece completely.

Preheat a large cast iron skillet or wok over medium-high heat. When the pan is hot, add the vegetable oil and let rest for 30 seconds.

Add the dredged chicken pieces to the pan (depending on the size of your skillet, you may need to work in batches). Fry the chicken pieces, stirring them often, until all sides are crispy and golden (about 5 minutes).

Add the sauce to the skillet and simmer for 1 to 2 minutes or until the sauce is thick.

Serve over rice. Garnish with sliced green onions and sesame seeds.