Place the seedless watermelon cubes in a large mixing bowl. Slice the cucumber thinly and add to the bowl. Gently toss to combine, ensuring even distribution of the fruit and vegetables.
Scatter the crumbled feta cheese over the top of the salad. Tear whole mint leaves and sprinkle them evenly across the mixture to release their aroma.
Drizzle the olive oil over the salad, then season with salt and freshly ground black pepper to taste. Gently toss again to combine all ingredients without breaking the watermelon or feta.
Transfer the salad to a serving plate or bowl, arranging attractively to showcase the colorful layers of watermelon, cucumber, and feta. Garnish with additional mint leaves if desired.