Use a chef's knife and cutting board to chop fresh mint leaves into small, even pieces.
Place watermelon cubes into a large mixing bowl, ensuring they are evenly distributed and free of excess moisture.
Add crumbled feta cheese to the watermelon in the bowl, stirring gently to combine without breaking the cubes.
Sprinkle the chopped mint leaves over the mixture, then fold everything together using a spoon or salad tongs until evenly combined.
Once combined, transfer the salad to a serving dish or bowl, and garnish with additional mint leaves if desired.