Heat the oven to 250 degrees F/120 degrees C.
Lay the fish fillets
in a baking dish
just large enough to hold them. Pour over enough oil to cover. Add the orange zest
, fennel seed
sprigs, garlic and some pepper. Bake until just tender, about 10 minutes. Remove the fish from the oil. Garnish with the fleur de sel
. Serve with a little of the cooking oil dribbled over.