01 - Preheat oven to 400°F. Line a baking sheet with parchment paper or lightly grease it.
02 - Season the chicken pieces with salt and pepper, then toss with cornstarch until evenly coated.
03 - Arrange the coated chicken in a single layer on the prepared baking sheet. Bake for 20 minutes, flipping halfway through, until golden and cooked through.
04 - While the chicken bakes, combine the orange juice, orange zest, soy sauce, rice vinegar, honey or brown sugar, minced garlic, grated ginger, sesame oil, and chili flakes in a saucepan. Bring to a simmer over medium heat and cook for 5 to 7 minutes, stirring frequently, until the sauce slightly thickens.
05 - Transfer the baked chicken to a large bowl. Pour the orange sauce over the chicken and toss to coat thoroughly.
06 - Return the sauced chicken to the oven for an additional 5 to 7 minutes until caramelized.
07 - Garnish with sliced green onions, sesame seeds, and orange slices if desired. Serve immediately with steamed rice or vegetables.