Peel onions and cut them into thin rings. Peel garlic and chop very finely. Mix crème fraîche, mustard, honey and garlic. Season strongly with salt and pepper. Crumble the bread between your hands.
Finely grate the parmesan. Drain the mozzarella and carefully squeeze the liquid out between kitchen paper. Cut mozzarella into slices. Wash the fish and dab dry. Place on a baking tray lined with baking paper.
Sprinkle with lemon juice. Spread onion rings evenly over the fish.
Spread honey-mustard cream over it. Mix parmesan and bread, sprinkle on the cream and cover with mozzarella. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for 20-30 minutes.
Meanwhile, wash the parsley, shake dry, pluck the leaves from the stalks and, except for a little to garnish, cut finely. Take the fish out of the oven and arrange on a plate, sprinkle with parsley and garnish.
Baguette tastes good with it.