Slice the cucumber very thinly. Use a mandoline for best results.

Place the cucumber slices in a bowl. Use your hands to unstick the slices that might stick together.

Chop the onion very finely and give it to the bowl together with the dill.

Place the vinegar, sugar, some salt, and pepper in a small bowl. Whisk to combine and add the oil. Whisk until the mixture emulsifies slightly.

Pour the vinaigrette over the salad and combine, preferably with your hands, this way you will be able to unstick even more cucumber slices and coat them nicely with the oil and vinegar dressing.

Adjust the taste with more salt, pepper, and sugar if necessary.

Serve as suggested above.