Preheat the oven to 180ºC, fan 160ºC, gas 4. Weigh the fish and calculate the cooking time. Wipe the gutted fish with kitchen paper. Using scissors, snip off the fins.
Take a large sheet of foil and liberally cover with butter.
Place a few slices of lemon on the foil with half the dill and half the peppercorns (save the other lemon to cut into wedges to serve). Lay the remaining dill, lemon slices, and peppercorns inside the salmon.
Take a second sheet of foil and scrunch into a sausage and place in the cavity of the salmon. Lift the prepared salmon onto the foil, with its spine uppermost, and give it a slight curve.
Pour the wine or stock over the fish.
Cover with another large sheet of well-buttered foil and scrunch the edges to create a roasting bag of foil.
Roast for 10 minutes per 450g. Remove from the oven and test. Push a knife into the thickest part of the fish and twist. Pull out some fish and check to see that it is opaque and hot to the touch. Use a sharp knife to run down the back of the fish to release the skin.
While the fish is still warm, using a round-bladed knife, carefully peel away the skin. Lift the fish onto a serving platter. Carefully remove the foil ‘sausage’ and spread mayonnaise over the fish. Arrange the cucumber discs over the salmon to look like scales. Arrange salad over the platter and garnish with lemon wedges and tomatoes.
Watch our How to video for a step by step guide