In a large mixing bowl, combine the onion, cilantro, basil, mint, lime juice, extra virgin olive oil, balsamic vinegar and a pinch of salt. Using a large spoon mix the ingredients together and let sit on the counter while you cut up your watermelon.
Add the cut watermelon to the large mixing bowl with the dressing at the bottom. Top with the feta cheese.
Using a large spoon, gently toss the watermelon and feta with the dressing at the bottom of the mixing bowl. After combined, transfer to a serving bowl.
Garnish with fresh mint and a thin slice of watermelon.
Serve immediately.
Garnish: Sprigs of fresh mint and a slice of watermelon