In a large bowl, add the watermelon, blueberries, cucumber, feta, and basil. Gently toss to combine.
In a small bowl, whisk together the vinegar, honey, and olive oil. Season with salt and pepper to taste.
Pour the dressing over the salad shortly before serving and gently toss to coat.
Serve immediately or chill briefly before serving.
Video
Notes
For best results, prepare the watermelon, cucumber, blueberries, feta, basil, and dressing separately up to 8 hours in advance. Toss everything together shortly before serving. Leftovers can be stored in an airtight container in the refrigerator for 1 to 2 days, but the salad will release liquid as it sits.