Wash the king oyster mushrooms thoroughly and cut them into bite-sized pieces.
Slice the onion into thin strips.
Heat some cooking oil in a pan over medium heat.
Add the onion first and stir-fry until translucent, then add the king oyster mushrooms.
Season with salt and pepper.
Stir-fry until the mushrooms are cooked through.
Transfer the finished stir-fry to a plate to serve.