Add the chicken to a bowl, along with the 1 tablespoon cornstarch and 1 tablespoon oil. Mix well and set aside.
Heat a wok over high heat until smoking. Add 2 tablespoons of oil, and the chicken. Stir-fry the chicken for 1-2 minutes, until well-seared.
Add the garlic, chilies (if using), bell pepper, scallions, chili sauce, and fish sauce. Stir-fry for another 2 minutes.
Serve with steamed jasmine rice.
