In a large mixing bowl, combine the cubed watermelon, sliced strawberries, blueberries, raspberries, and chopped mint leaves. Gently toss to combine.
In a small bowl, whisk together the lime juice, honey (or agave syrup), lime zest, and a pinch of salt until well blended.
Drizzle the lime dressing over the fruit salad and toss gently to coat all the fruit evenly.
Refrigerate the salad for at least 30 minutes to allow the flavors to meld and the salad to chill.
Serve chilled, garnished with additional mint leaves if desired.