In a medium saucepan over low/medium heat add two tablespoons of vegetable oil, followed by the garlic and ginger, cook and stir for 30 seconds and whisk in the brown sugar, red pepper flakes, soy sauce, rice vinegar, and water. Cook until slightly thickened, about 5-10 minutes, set aside.

Meanwhile, mix chicken with the cornstarch until evenly distributed.

Heat vegetable oil in a large saucepan, once hot add the chicken and fry until browned and cooked through about 1-2 minutes. Stir the meat around a little so that it cooks evenly. Transfer chicken to a paper towel-lined plate and discard the oil from the skillet.

Add chicken back to the skillet, add the soy sauce mixture and cook over medium heat until sauce thickens about 2-3 minutes.

Stir in green onions. Garnish with sesame seeds (optional).

Serve immediately over rice.