Heat the oil in a wok or frying pan over medium heat and stir-fry the mushrooms and chives for 2 minutes.
Melt the miso paste in water, add to the frying pan and stir until the liquid has evaporated. Pour the eggs over the mushrooms and swirl the frying pan to make a thin omelet. Bake the omelet for 1 minute, remove from the skillet and roll up. Sprinkle with pepper and bring to the table.