First prepare the dressing. To do this, stir together vinegar, oil, spices and raspberry buttermilk. Water is not necessary, as the lettuce will still draw some water when it is steeped.
Peel the cucumber if necessary, slice it into thin slices and cut the spring onion finely. Put everything in a bowl and mix in the dressing. Let it steep for half an hour to an hour. Sprinkle some dill on top, if desired.