Cut off the root ends of the enoki mushrooms and rinse them under running water.
Slice the onion into thin strips.
Add cooking oil to a pan and preheat over medium heat.
Add the onions first and stir-fry for 1–2 minutes.
Add the enoki mushrooms and stir-fry for another 2–3 minutes.
Season with salt and pepper, and mix well.
Transfer the finished stir-fry to a plate.