Let the cooked prawns drain well and pat them dry with kitchen paper.
Cut the cucumber into half-moons and the avocado into chunks. Put them together with the prawns in a bowl.
Chop the dill finely and make a dressing from the olive oil, lime juice, salt and pepper.
Pour the dressing over the salad, add the dill and toss everything gently so the avocado stays whole. Serve the salad cool on a plate.