In a large mixing bowl, combine the cubed watermelon and diced cucumber.
Add the crumbled feta and sliced red onion to the bowl.
In a separate small bowl, whisk together the olive oil, balsamic vinegar, salt, and pepper until emulsified.
Drizzle the dressing over the watermelon mixture.
Gently toss everything to combine, making sure not to break up the feta too much.
Sprinkle the chopped mint leaves on top and give it one last gentle stir.
Adjust seasoning with more salt and pepper if desired.
Chill in the refrigerator for about 20 minutes to allow flavors to meld before serving.
Notes
Serve the salad in a large clear bowl to showcase the beautiful colors, or portion into individual plates. Garnish with extra mint leaves for a refreshing touch.