To prepare, first reduce the balsamic vinegar to a syrup by simmering the vinegar in a saucepan over medium heat for about 10 minutes. When reduced to approximately ¼ cup transfer the balsamic syrup to a small cup and set aside.

Cut watermelon in ¾ inch thick triangles, and cut the feta cheese in triangles as well. Assemble on platter, either stacking or overlapping the watermelon and feta triangles. Sprinkle mint chiffonade on top and drizzle with balsamic syrup.