Cut the beef short ribs into bite-sized pieces.
Wash the mushrooms thoroughly and chop them into manageable pieces.
Julienne the onion and green onion.
Heat cooking oil in a pan and stir-fry the beef short ribs.
Season the beef with salt and pepper.
Add the mushrooms, onion, and green onion, then stir-fry them together.
Add soy sauce and sesame oil, mixing well to combine.
Once the mushrooms are cooked through, turn off the heat and serve.