Wash the vegetables (lettuce, tomato, cucumber) carefully. Slice the cucumber, tomato, and half of the red onion thinly. Dice the remaining red onion.
Marinate the red onion slices with sugar and vinegar for 15 minutes.
Season the ground meat with the diced red onion, ground pepper, salt, soy sauce, chili powder, egg, chili sauce, ketchup, and oyster sauce. Mix well and marinate for 5 minutes.
Preheat your air fryer for a few minutes.
Brush cooking oil on the basket.
Divide the ground meat mixture into 4 equal parts. Roll the meat into balls and press them between your palms into patties.
Place the patties into the air fryer basket and brush them with olive oil. Air fry the patties in u0022beefsteak modeu0022 or at 400 degrees F for 6 minutes.
Flip the patties, brush them with olive oil, and air fry them for another 6 minutes at 400 degrees F.
Top each patty with one (or a few) cheddar cheese slices and air fry them for 1 minute at the same temperature.
Cut the burger buns in half horizontally. Add the lettuce, tomato, cucumber, and patty to the bottom half. Next, add chili sauce and mayonnaise, and finish with a few slices of red onion.Place the top half over the onions, and enjoy!