Preheat the oven at 180 degrees C
Cut the potatoes and onions in thin slices
Put the potatoes and onion on an oven tray, add salt and coat with olive oil
Place in the Oven for about 30 min, or until the potatoes are soft but not brown
Make three cuts on each fish and introduce a slide of lemon. Add salt
Once the potatoes are soft, place the fish on top and add the white wine. Bake for another 15 to 20 min.