Cut the watermelon into 1-inch cubes and place in a large bowl. Dice the cucumber into similar-sized pieces and add to the bowl. Thinly slice the red onion into slivers and add it as well. Roughly chop the mint and basil leaves, keeping them separate for now—I find that adding fresh herbs at the end preserves their bright flavor better than mixing them in early.
In a jar with a tight-fitting lid, combine the honey, freshly squeezed lime juice, olive oil, and salt. Seal the jar and shake vigorously for about 10-15 seconds until the honey dissolves completely and the dressing emulsifies slightly. The shaking helps the honey incorporate smoothly rather than settling at the bottom.
Crumble the feta cheese into bite-sized pieces directly over the bowl of watermelon and vegetables. Pour the dressing from Step 2 over the salad and add the black pepper. Gently toss everything together until the vegetables are evenly coated with the dressing, being careful not to crush the watermelon pieces or over-mix the feta.
Add the chopped mint and basil from Step 1 to the salad and give it one final gentle toss to distribute the herbs throughout. Serve immediately while the watermelon is still chilled and the herbs are at their freshest.