Cut the chicken thighs into bite-sized pieces and mix flour, salt, and pepper in a bowl. Dredge chicken in the flour mixture.
In a saucepan, combine orange juice, sugar, soy sauce, rice vinegar, garlic, ginger, and red pepper flakes. Simmer and thicken with cornstarch mixed with water.
Coat chicken pieces in beaten eggs and then roll in panko breadcrumbs. Set aside.
Heat vegetable oil in a skillet and fry chicken in batches for 5-7 minutes until golden brown. Drain on paper towels.
Toss fried chicken with orange sauce until well coated and serve immediately.