Make the dressing: In a small bowl, whisk together the honey, juice from one lime, olive oil, salt and pepper. Taste it, the lime juice should be coming through, so add the second lime if needed. Thinly slice small red onion and add to dressing. Set aside.
Make the Salad: In a large serving bowl, combine the watermelon, cucumber, mint, basil, and ¼ cup of the feta.
Top the watermelon salad with the dressing and gently toss to combine.
Top with the remaining feta cheese and sumac and serve right away.
