1 lb thin skinned, mild (non bitter) cucumbers, such as Persian, Armenian, or Japanese cucumbers, thinly sliced. You might also try it with english cucumbers.
1/4 red onion, thinly sliced and cut into 1-inch long segments
2 or 3 red radishes, thinly sliced
10 mint leaves, thinly sliced
1/4 lb feta cheese
salt and freshly ground pepper