Drizzle the lemon juice over the fish, fry the onions in olive oil until soft. Layer the fish, vegetables + mushrooms in a greased (olive oil) baking dish. Salt + pepper, sprinkle with capers, cover and bake for 15 minutes in a preheated oven, 160 ° C fan oven.
Grate the cheese, sprinkle over it, cook for another 5 minutes until the cheese runs off.
Layer potatoes with them or in the baking dish first, cooked millet, or cooked rice or cooked buckwheat are also suitable, but I have already taken cooked amaranth.