Preheat the oven to 180°C.
Rub the fish with some oil,then season with salt and pepper.
Cut the lemon into thin rings.
Rub the base of a roasting tray with butter or oil, then lay half of the lemon disks in two rows. Place the fish on top.
Cut the rest of the lemon into two halves and put these inside the fish. Divide the dill between the two fish.
Add a drop of water or white wine to the pan, cover with foil and bake for 15-25 minutes.
Turn up the heat or set to the grill and brown the skin for a couple of minutes.