Halve the tomatoes, cut out the stalk and cut into eighths in total. Scrape the seeds out of the cucumber, halved lengthways, and cut into slices like the peeled onions. Roughly chop the washed parsley and mix everything together with the olives in a bowl.
Season the lemon juice with salt, pepper and sugar and stir in the oil, pour over the salad and let it steep in the refrigerator for about 20 minutes.