Peel and slice the red onion into rings. Place in a bowl. Drizzle over Greek wine vinegar and a little chilled cold water. Set aside for 15 minutes to allow the heat from the onion soften. After 10 minutes, drain off the liquid and reserve the onion.
Wash and peel the cucumbers. Run the tines of the fork along the edges of the cucumbers to create ridges to catch the dressing. Cut into rounds. Place the cucumbers into the bowl with the onions.
Wash and core the two large tomatoes. Slice into wedges. Be sure to cut the tomatoes over the salad bowl, to catch all of the summery juices. Place the cut tomatoes into the bowl with the cucmbers. Wash and halve the cherry tomatoes and place in the bowl.
Add the olives and toss the salad ingredients to combine well. At this point, it is best to put the salad in the fridge to chill well until you are ready to serve.
When ready to serve, add salt to taste, followed by a good drizzle of Greek wine vinegar. Finally add a generous glug of extra virgin olive oil (more than you think you need!) and toss the salad to combine. Check the seasoning and add a grinding of black pepper, if preferred. Then top with the whole slice of feta and another glug of extra virgin olive oil. Sprinkle generously with dried oregano.
When the salad is nearly finished and only those glorious summer juices and olive oil remain in the bowl, do as Kosta does on holidays - add a little drop of ouzo and mop up with a good slice of rustic sourdough bread.