Combine soy sauce, honey, sesame oil, and mirin in a bowl and mix until the honey is dissolved. Use a basting brush to baste half of this sauce on the flesh of the fish (reserve the other half). Place a seasoned cast iron skillet on high heat and when hot, place the fish in it, skin-side up.

Cook fish for 2 minutes and then pour over the remaining glaze. Cook for another 2 minutes or until the flesh has been charred but not burnt. Flip fish so it is skin-side down and cook for another 2 minutes or until it flakes easily. If fish is not cooked through at this point, you can place it in a 400 degree oven for a few minutes.