In a large bowl, whisk together lime juice, sugar, rum, and salt.
Using a melon baller, scoop melon into balls (you'll get about 10 cups), or cut melon into bite-size chunks. Add melon to lime mixture in bowl. Sprinkle with mint and lime zest, and toss gently to combine. Serve immediately, or cover and refrigerate, up to 2 hours.
Fabulous! Quick, easy, light, refreshing. I think it makes more than 6 servings.