Boil the egg hard, let it cool, chop finely, set aside. Cut the pitted, peeled cucumber into fine slices. Cut the peeled kohlrabi into thin sticks 5 cm long. Finely dice the onion.
Mix the vinegar, salt, pepper, sugar and oil into a vinaigrette. Let the cucumber, kohlrabi, onion and frozen peas stand in the vinaigrette for 30 minutes.
Tear apart the lollobianco, cut into bite-sized pieces, wash and spin dry. Finely chop the parsley. Mix with the remaining ingredients with the salad and arrange everything on a plate.
Pluck the trout into pieces and spread them over the salad with the chopped egg.
If I know in advance that the salad has to stand for a really long time, I replace the lollobianco with iceberg lettuce.