Peel the onion and cut into thin rings. Wash the tomatoes, quarter them and remove the stalks. Peel the cucumber, cut it in half lengthways (remove larger seeds if necessary) and cut into 4 - 5 mm thick slices. Halve the peppers, remove the stems, remove the seeds, wash and cut into thin strips. Dice the sheep cheese. Put everything - together with the olives - in a bowl. Mix a marinade from the water, white wine vinegar, olive oil, salt, oregano and pepper and pour over the salad. Mix carefully but well with salad servers or similar. White pastries such as flatbread and baguette go particularly well with this refreshing salad from southern Europe.