For the dressing, squeeze about one tablespoon of grapefruit juice into a bowl (reserve the segments). Add the remaining dressing ingredients and stir well to combine.
For the salad, add the grapefruit segments, lettuce and chickpeas to the dressing and toss well to coat.
Pile the salad onto a serving plate and sprinkle over the flaked salmon. Stir the chervil in with any remaining dressing and spoon around the edge of the plate. Squeeze over the lemon juice to serve.
