Mix together the first 5 ingredients with just enough water to make a fairly thick marinade—about the consistency of ketchup.

Pour the marinade into a zip-locked plastic bag and chill.

When the marinade is cold, place the fillets into the bag, making sure they’re coated with the mixture. Return to fridge. The longer you marinate, the more miso flavor the fish will absorb. Two hours is a good amount of time to begin with, but a full day is not too long.

Prepare the grill.

Add about 1 tablespoon of olive oil to a piece of flat aluminum foil large enough to hold the fillets, folding up the edges to retain the oil. Place this on the grill and heat to sizzling.

Remove the fillets from the marinade. Let excess mixture drip off. It is not necessary to rinse the fillets. Place the fillets on the hot aluminum, skin side down. Make certain the foil is very hot to prevent the fish from sticking.

A good rule of thumb when cooking fish on a hot grill is 10 minutes cooking time per inch of thickness. With 1-inch-thick fillets, cook skin side down for 7 minutes. Then, gently flip the fillet and cook for 3 minutes to finish.

Serve immediately on a bed of rice. You might want to provide a wedge of lemon to spritz the fillet with, but try it without the lemon first.