Rinse the fennel bulbs, cut into thin slices or shave and bring to the boil briefly with vegetable stock and vinegar in a sauté pan. Remove the fennel, reserve the stock and allow both to cool.
Squeeze the lemon and stir the juice into the stock together with the olive oil. Season with salt and pepper from the mill.
Cut the tomatoes into cubes, finely weigh the fennel and mix with the fennel strips. Arrange together with very thin slices of salmon and drizzle evenly with the sauce. Garnish with lettuce to taste.