Season chicken pieces with salt and pepper.
Toss them in flour, dip into beaten eggs, then coat with cornstarch.
Heat oil in a pan over medium-high. Fry chicken in batches until crispy and golden.
In another pan, combine soy sauce, vinegar, brown sugar, ketchup, garlic, and ginger.
Bring to a simmer and stir in the cornstarch slurry.
Let it thicken, then stir in sesame oil.
Toss crispy chicken into the sauce until coated evenly.
Garnish with sesame seeds and sliced green onions before serving.