Preheat the oven to Gas 4, 180ºC, fan 160ºC.
Cut the crusts off the bread and discard them. Place the bread, the hazelnuts, the parsley and the lemon rind in a liquidiser or food processor and blend until finely chopped. Season.
Place the trout, skin-side down, on a lightly oiled baking dish and press the nut mixture over. Bake for 12-14 minutes until the fish is firm and the crumbs are a light golden brown.
This is delicious served with sliced new potatoes, green beans and a wedge of lemon.