Toss chicken pieces with cornstarch until coated evenly.
Heat oil in a skillet over medium heat and cook the chicken until golden and crispy. Remove and set aside.
In the same skillet, sauté garlic and ginger for about 30 seconds.
Add soy sauce, water, brown sugar, and red pepper flakes. Stir well and bring to a simmer.
Let the sauce bubble for 2–3 minutes until slightly thickened.
Return chicken to the skillet and coat with the sauce.
Top with green onions and sesame seeds before serving. Best over rice or noodles.