Dust the tofu with potato starch, shake off excess. Heat the vegetable oil in a pan, put tofu in it and fry until crisp over medium heat. Add onion and stir fry until cooked.
Pour in the sauce (*) and cook for 2~3 mins over medium heat.
Pour in the beaten egg and mizuna and cook with a lid. To finish it off, pour sesame oil from the edge of the pan to inside of it. Turn off the heat when becomes desired hardness of the eggs. (adjust the hardness of the egg with the remaining heat)