Wash the cucumber as well, peel it if necessary, and cut it into cubes.
For the sauce, stir the herb quark, tuna, oil and mustard until smooth. Season well with salt and pepper. Stir in lemon juice and season to taste again. Add the lettuce and cucumber to the sauce and mix everything well.
The salad is very variable in terms of the salad ingredients. Radishes also go very well with the fish.