Trim the root of the shimeji mushrooms and separate into small clusters. Reserve 9 small clusters for garnish and finely chop the rest.

Place ground pork, chopped mushrooms, and seasoning ingredients (marked with ☆) into a plastic bag. Knead the mixture through the bag until it becomes sticky.

Spread salad oil thinly in a tamagoyaki pan using a paper towel. Add the meat mixture and flatten it evenly. Place the reserved mushroom clusters on top and press lightly. Cook over medium heat for about 3 minutes until lightly browned.

Flip the meat mixture using a heatproof plate and return it to the pan. Cover with aluminum foil and cook over low-medium heat for 5 minutes until fully cooked. Remove the foil and cook over high heat for 1 minute. Let it cool slightly.

Wipe the pan clean with a paper towel and add the sauce ingredients (marked with ★). Heat over medium heat until boiling and thickened.