Mince the white part of the green onion.

In a bowl, mix the natto with its included sauce and mustard, then add the minced green onion and mix again.

In a separate bowl, crack the eggs, add salt, and whisk to make beaten eggs.

Heat vegetable oil in a frying pan over medium heat, pour in the beaten eggs, and stir gently until half-cooked. Place the natto mixture in the center, fold the eggs over to wrap the filling, and shape the omelette.