Heat sesame oil in a wok or large skillet over low heat. Cook and stir onion and garlic until soft, about 5 minutes. Add bok choy and continue to stir-fry. Add soy sauce, fish sauce, pine nuts, toasted sesame seeds and Thai basil. Stir-fry until the green tips of the bok choy and the basil are just wilted, about 3 minutes.