Cut watermelon into two-inch thick slices. Using a cookie/biscuit cutter, cut watermelon into circles.
Use a melon baller to scoop out the center of the watermelon circles to create a cup.
In a medium glass bowl combine diced cucumber, feta, mint, and balsamic.
Fill cups with diced cucumber, feta cheese and mint.
Drizzle with additional balsamic vinegar if desired, and enjoy!