Combine the sliced chicken with the cornstarch and 1 teaspoon vegetable oil.
Heat 1 tablespoon oil in a wok over high heat. Add the chicken, and stir-fry until opaque. Remove the chicken from the wok and set aside.
Add another tablespoon of oil in the wok, and add the garlic, onion, and chilies. Stir-fry for 1 minute. Add the reserved chicken, soy sauce, dark soy sauce, oyster sauce, fish sauce, sugar, Thai basil, and mint.
Stir-fry for about 30 seconds, until the basil and mint leaves are wilted. Serve immediately with steamed rice.