Onions peel and in thin rings planes and/or cut. Peel garlic and chop very finely. Mix crème fraîche, mustard, honey and garlic. Season with salt and pepper.
Line a baking tray with baking paper. Preheat the oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Crumble bread between your hands. Grate parmesan finely. Mix bread and Parmesan.
Drain mozzarella well and cut into thin slices. Rinse salmon, dab dry and place on the tray. Sprinkle with lemon juice, season with a little salt. Spread onion rings all over the salmon.
Spread honey-mustard cream on top. Spread the parmesan bread mix over the cream and cover with mozzarella. Bake in a hot oven for 20-30 minutes.
Meanwhile wash parsley, shake dry, pluck leaves from the stalks and chop finely. Remove salmon from the oven, arrange on a plate and sprinkle with parsley. Serve with baguette and lettuce.