Cut the atsu-age into 1 cm pieces.

Slice king oyster mushrooms into 5 cm diagonals.

Slice Japanese leeks into 5 cm diagonals.

Cut the pork into easy-to-eat pieces.

Mix oyster sauce, soy sauce, mirin, sugar, sake, water, grated ginger, and katakuriko together in a bowl.

Heat sesame oil in a frying pan over medium-high heat.

Add pork to the pan and season lightly with salt and pepper.

Sauté the pork until lightly browned.

Add the atsu-age, king oyster mushrooms, and Japanese leeks to the pan.

Sauté the mixture until the vegetables are tender.

Reduce heat to low.

Pour the oyster sauce mixture over the ingredients.

Stir continuously to coat all ingredients with the sauce.

Continue stirring until the sauce thickens.

Serve immediately.