Make the sauce: Zest the orange and squeeze to get 1/2 cup juice. Whisk together orange juice, zest, soy sauce, brown sugar, rice vinegar, grated ginger, minced garlic, red pepper flakes, and 1/2 Tbsp corn starch until fully dissolved.

Cut the chicken: Trim excess fat from chicken thighs and cut into 3/4-inch pieces.

Coat the chicken: In a mixing bowl, whisk together the egg, 2 Tbsp corn starch, and a pinch of salt and pepper until smooth. Add chicken pieces and stir to coat completely.

Brown the chicken: Heat a large skillet over medium-high heat with 2 Tbsp cooking oil. Add chicken in a single layer and cook until golden brown on the bottom, about 5-7 minutes.

Flip and cook: Flip the chicken pieces and cook for another 2-3 minutes until cooked through and golden brown.

Add sauce: Pour the prepared orange sauce over the cooked chicken in the skillet. Stir continuously as the sauce simmers and thickens for about 1-2 minutes.

Serve: Remove from heat and serve immediately over steamed rice, garnished with extra orange zest or sesame seeds if desired.