In a large mixing bowl, combine the cubed watermelon, diced cucumber, and chopped mint leaves.
Drizzle the olive oil over the mixture.
Sprinkle with kosher salt and black pepper.
Gently toss until all ingredients are lightly coated.
Add the crumbled feta cheese and toss carefully to distribute evenly without breaking up the watermelon.
Transfer the Watermelon Feta Cucumber Salad to a serving bowl or platter.
Just before serving, drizzle the balsamic glaze evenly over the top.
Garnish with additional mint leaves if desired.
Serve immediately while chilled for the best flavor and texture.