Peel the cucumber, halve it lengthwise and remove the seeds. For the dressing, roughly dice one cucumber half. Clean the chilli, cut lengthwise, remove seeds, wash and cut into fine rings. Peel and chop ginger.
Finely puree the cucumber cubes, ginger, orange juice, fish sauce and sugar with a hand blender. Stir in the chilli. Season to taste with salt and pepper.
Rinse the crayfish meat briefly and drain well. Clean, wash and shake the salad dry. Put 4 leaves aside. Chop the rest of the lettuce and the other half of the cucumber. Wash coriander, shake dry and remove the leaves.
Cut the avocado in half, remove the stone. Peel the avocado, cut off 8 very thin slices and sprinkle with lime juice. Chop the rest of the avocado. Mix with chopped lettuce, cucumber, coriander and cucumber dressing.
Serve with avocado wedges and crayfish on the salad leaves.