Wash the soybean sprouts thoroughly and remove the heads.
Slice the green onion and onion into thin strips.
Heat cooking oil in a pan and stir-fry the green onion to release its aroma.
Add the onion and soybean sprouts, and stir-fry over medium heat.
Season with salt, soy sauce, and pepper.
Once the soybean sprouts are cooked, turn off the heat and transfer to a plate.