Score the duck skin, rub all over with sea salt and black pepper, then place skin side down in a large non-stick frying pan on a medium-high heat.
Sear for 6 minutes, or until the skin is dark golden, then turn and cook for 5 minutes, or to your liking.
Remove to a board to rest, leaving the pan on the heat.
Slice 10 thin slices of baguette (keeping the rest for another day).
Place in the hot pan with the walnuts to toast and get golden in the duck fat, then remove and arrange the toasts on your plates.
Meanwhile, top and tail the oranges, cut away the peel, then finely slice into rounds (removing any pips).
Finely slice the duck, place on the toasts, dotting any extra slices in between, then add the oranges in and around.
Dress the watercress with any resting juices on the board, then sprinkle over.
Finely grate or crumble over the walnuts, sprinkle from a height with a little extra seasoning, and serve.