Prepare the Chicken:
In a bowl, season chicken pieces with salt and pepper. Toss with cornstarch until evenly coated.
Fry the Chicken:
Heat about 1 inch of oil in a deep skillet or pan over medium-high heat. Fry chicken in batches for 3–4 minutes until golden and crispy. Drain on paper towels.
Make the Sauce:
In a small bowl, whisk together soy sauce, rice vinegar, hoisin sauce, water, and sugar. Set aside.
Cook the Sauce:
In a clean skillet, heat a small amount of oil over medium heat. Add garlic, ginger, and red pepper flakes. Sauté for 30 seconds until fragrant. Pour in the sauce mixture and bring to a simmer.
Thicken the Sauce:
Stir in the cornstarch slurry and cook for 1–2 minutes until the sauce thickens to a glaze.
Combine Chicken and Sauce:
Add the fried chicken to the skillet and toss to coat evenly in the sauce.
Serve:
Garnish with green onions and sesame seeds. Serve immediately with steamed rice or stir-fried vegetables.