Combine olive oil, lime juice, sugar, and salt in a small bowl. Whisk together until sugar is dissolved.
Add watermelon, onion, feta, and mint to a large bowl.
Pour dressing over salad, then mix gently. Adjust seasoning with additional salt, if desired.
Serve immediately. Enjoy!
Watermelon releases lots of liquid after its cut, so this salad is best eaten shortly after making. If you do prepare it ahead of time (or if you have leftovers), you may want to drain some of the liquid before serving.This recipe is really flexible. Feel free to add other ingredients, serve over greens, or change up the dressing. See tips before the recipe for lots of ideas.