Combine the lemon juice with half the oil along with some salt, pepper, and the chervil. Arrange the salmon slices on a plate in a single layer and spoon the sauce over the top. Refrigerate for 4 to 6 hours.
Cook the fava beans in boiling water for 5 minutes. Drain. Chill in an ice bath. Remove skins from the beans and discard. Drain the beans and set aside until needed.