I used righteye flounder, but I also recommend haddock.
Top the fish with all of the ingredients except the ponzu.
Twist both ends of the foil tightly closed.
Pour in the ponzu. Since the enoki mushrooms will release water and thin out the flavor, if you would like a stronger taste, adjust the amount accordingly.
Fold over the aluminum foil and wrap up the ingredients. Place in a frying pan filled with 1 cm of water.
When it comes to a boil, lower the heat to low and cover with a lid to steam for 15 minutes. Then it's done.