In a blender (or immersion blender) liquefy lemon juice, mint leaves, olive oil, salt and a bit of pepper. Dress salad immediately, or dressing can be made 1 day ahead and kept covered in the refrigerator.

In a large bowl, with a spatula, mix gently the cubes of watermelon, tomato, plum and the greens. Drizzle in dressing and make sure all fruits and vegetables are evenly covered.

Sprinkle crumbles of feta cheese on salad and top with a bit of freshly ground pepper.

Serve immediately or refrigerate for up to two hours (although the greens might wilt a bit, but the fruits will have a chance to marinate a bit more in the dressing, making them more flavorful).