Thinly slice 1 scallion on a steep bias. Submerge the sliced scallions in a bowl of ice water to encourage them to curl.
In a small bowl, whisk together 1 tbsp soy sauce, 1 tsp mirin, 1 tsp yuzu kosho, and 1 tbsp rice vinegar.
Set the monkfish liver pieces on a plate and pour the sauce over the monkfish. Shake off the water from the sliced scallions and set on top of the monkfish as garnish.