Cut beef against the grain, add salt, light soy sauce, oyster sauce, white pepper, water and cornstarch. Mix well until well combined. Then add vegetable cooking oil, remixing again. Set aside.
Wash, drain, and cut the lettuce into long sections. Then, roughly mince the garlic and cut the Thai pepper into circles.
Heat your wok, then add vegetable oil. Add the beef in when the oil is still warm but not hot, cook until the beef slices change color, and transfer them out.
Leave the oil in, fry garlic and Thai pepper until aromatic.
Add the lettuce in.
Lastly, return cooked beef slices, pepper flakes, salt, light soy sauce, and rice wine. Fry for a while and drizzle sesame oil to coat.