Wash the king oyster mushrooms thoroughly and cut them into bite-sized pieces.
Julienne the onion and green onion.
Heat some cooking oil in a pan over medium heat.
Add the onion and green onion first and stir-fry.
Add the king oyster mushrooms and season with salt and pepper.
Stir-fry until the mushrooms are cooked, then drizzle with sesame oil to finish.