Peel and thinly slice the ginger and garlic. Cut the mushroom into strips. Slice the spring onion thinly and diagonally.
In a wok, or frying pan, heat the sesame oil. When it starts smoking, add the ginger and garlic slices, brown them slightly. Add the mushrooms and stir for two minutes, then pour in the soy sauce and add the sugar. Stir for a minute, then take it off the heat.
Mix the wasabi with the mayonnaise.
Mix the egg lightly with the salt.
Oil a large, stainless steel ladle and heat it over the gas flame. Add a Tbspful of egg and tilt the ladle to allow the egg to coat the inner surface of the ladle. Hold the ladle over the flame. When the edge of the omelette starts coming away from the ladle and the surface of it is shiny, remove it carefully from the ladle, using a knife or small spatula.
Repeat this process with the remaining eggs.
Place 2-3 egg nests into each other, spread some wasabi mayo around and fill with the mushroom mixture. Serve with spring onions and bean sprouts sprinkled on the top