Begin by marinating the chicken pieces in soy sauce and brown sugar for 10 minutes.
In a bowl, mix cornstarch with a little water to create a slurry.
Heat vegetable oil in a large skillet over medium-high heat.
Add minced garlic and ginger to the skillet, sautéing for 1-2 minutes.
Add the marinated chicken to the skillet, cooking until browned (about 5-7 minutes).
Pour in the remaining marinade and bring to a simmer.
Stir in the cornstarch slurry to thicken the sauce.
Add red pepper flakes if desired for extra heat.
Cook for an additional 3-5 minutes, until the sauce is glossy and thick.
Garnish with sliced green onions and sesame seeds before serving.