Wash the king oyster mushrooms thoroughly and slice them thickly.
Cut the onion and green onion into bite-sized pieces.
Heat cooking oil in a pan and stir-fry the green onion first to bring out the aroma.
Add the onion and king oyster mushrooms, then stir-fry together.
Add oyster sauce, low-sugar soy sauce, and pepper, and stir-fry quickly over high heat.
When everything is well mixed, turn off the heat and serve on a plate.