Fillet the fish (or let the fish vendor do this for you). Season the fillets with salt and pepper. Set aside.
Place the fish head and bone in a pot. Cover with water. Season with salt and pepper. Bring to the boil. Lower the heat, cover and simmer. Do not turn off the heat.
In another pan, heat the butter. Saute the button mushrooms just until lightly browned. Scoop out the mushrooms and set aside.
Add about 2 tbsps. of olive oil to the butter in the pan. Cook the onions over medium heat until translucent.
Pour in the rice. Stir until every grain is glistening with oil.
Add a generous splash of dry white wine. Allow to boil until the wine has been absorbed by the rice.
Ladle in a cup of simmering fish broth, stirring the rice until the liquid has been absorbed. Add another cup of broth, again, stirring until the rice has absorbed most of it. Season with salt and pepper as you cook, tasting occasionally.
Repeat until the rice is almost done. The level of doneness is such that when biting a grain, there should be the slightest resistance at the center. In pasta lingo, it's al dente.
When the rice has ALMOST reached that level of doneness, stir in the wood ears mushrooms.
When the rice is done, stir in the cheese and button mushrooms.
Pour in the lemon juice and give the risotto a quick stir. Taste. Adjust the seasonings, if needed. Stir in the parsley.
Keep the risotto warm.
Brush the fish fillets with olive oil and grill in a hot pan just until done, about three minutes per side.
Ladle risotto in a bowl, top with a grilled fish fillet, garnish with scallions and lemon zest, and serve.