Place the fish onto greased foil on a baking tray and season.
Place the sliced leek with a knob of butter or splash of oil in a small pan and gently saute until soft. Alternatively place the sliced leeks with the oil or butter in a microwaveable dish and cook in the microwave on high for approx. 3 minutes or until soft.
Cover the fish with a thin layer of crème fraiche, sliced cooked leeks and grated cheese.
Sprinkle with a thin crust of breadcrumbs and a few drops of oil.
Bake in the oven at 200°C/Gas Mark 6 for approx.15 minutes or until cooked through and golden brown.