In a small bowl, whisk together the cornstarch and soy sauce to make a slurry. Set the slurry aside.
Add the vegetable oil to a large saucepan set over medium heat. Once the oil is hot, add the chilies, garlic and ginger and cook, stirring constantly, until the garlic is golden brown, about 1 minute.
Stir in the rice wine vinegar, hoisin, brown sugar, chicken stock and sesame oil.
Stir in the slurry, bring the sauce to a simmer and cook it until it thickens to the consistency of syrup, about 1 minute.
Return the chicken to the pan and toss to coat.
Serve the chicken topped with scallions.