Cut the flesh from the melon and cut into bite-size pieces, removing and discarding any seeds. Place
watermelon pieces in a large serving bowl.
Peel and slice the onion into rings. Gently combine the onion rings and watermelon together.
In a small bowl, combine the vinegar, salt, and pepper; whisk until salt is dissolved. Slowly whisk in the olive oil, a few drops at a time. Add in the
chopped mint, taste, and adjust seasonings. Pour the dressing over the melon/onion mixture and toss gently until everything is coated and evenly mixed.
To serve, divide salad among individual plates and garnish with mint leaves.