In a large mixing bowl, coat the chicken pieces with cornstarch until fully covered.

Heat the vegetable oil in a frying pan or wok over medium-high heat until hot.

Carefully add the coated chicken pieces to the hot oil in batches, frying them until golden brown and cooked through (about 4-5 minutes per batch). Transfer to a paper towel-lined plate to drain excess oil.

In the same pan, add the minced garlic, ginger, and red chili flakes. Stir-fry for about 1 minute until fragrant.

In a separate saucepan, combine soy sauce, rice vinegar, sugar, chicken broth, and sesame oil. Bring to a gentle simmer over medium heat.

Stir the cornstarch-water mixture into the sauce, cooking until it thickens (about 2-3 minutes).

Add the crispy chicken to the pan with garlic and ginger. Pour the thickened sauce over the chicken, tossing well to coat evenly.

Garnish with sliced green onions and additional chili flakes if desired. Serve hot over steamed rice.