Cut the beef into ¾ inch cubes, always cutting against the grain. This is the most important step. Cutting against the grain shortens the muscle fibers so your beef stays tender instead of chewy.
Place beef in a bowl. Add soy sauce, oyster sauce, cornstarch, cooking oil, cumin powder, Sichuan peppercorn powder, and chili pepper powder.
Mix thoroughly with gloves or chopsticks until every cube is evenly coated. The cornstarch and oil will make the marinade slightly thick and sticky. This is exactly what you want.
Let the beef marinate for at least 10 minutes at room temperature.
Optional: Thread the beef cubes onto small skewers for a true night market presentation. Or simply spread the beef in a single layer in the air fryer basket. Do not pile them up or they will steam instead of char.
Lightly spray the beef with cooking oil. Air fry at 400°F (200°C) for 8 to 9 minutes total. At the 4 minute mark, open the air fryer and flip each piece so all sides get a beautiful char.
Serve immediately. Sprinkle with extra cumin or chili if desired.