You may not think to serve sweet watermelon with salty feta cheese, but the combination is actually quite tasty and refreshing. It is also a greek favorite in the summer and is eaten as a snack or a light meal. This variation includes paper-thin slices of red onion and a touch of balsamic vinegar to turn this fabulous taste combination into something truly memorable. This salad is the perfect dish to bring to a cookout or picnic since there is no lettuce that will get soggy. It is also a bit out of the ordinary and will add color to any buffet table while offering guests something different and delicious.