01 - Toss chicken pieces with cornstarch, salt, and black pepper in a large bowl until evenly coated.
02 - Heat vegetable oil in a large skillet or wok over medium-high heat. Add chicken in batches and cook until golden brown and crisp on all sides, about 6-8 minutes. Remove and set aside on a plate.
03 - Whisk together soy sauce, brown sugar, water, hoisin sauce, rice vinegar, and sesame oil in a medium bowl.
04 - Add ginger and garlic to the same skillet. Sauté for 1 minute until fragrant.
05 - Pour in the prepared sauce and bring to a simmer over medium heat. Cook for 2-3 minutes, stirring frequently, until slightly thickened.
06 - Add cooked chicken back into the skillet. Toss to coat evenly in the sauce. Add red chili flakes if desired.
07 - Simmer for an additional 2-3 minutes until the sauce clings to the chicken and the chicken is heated through.
08 - Serve hot over steamed rice. Garnish with sliced green onions and toasted sesame seeds.