Combine watermelon, cucumbers and feta in a large bowl. Mix together well with clean hands.
Combine all vinaigrette ingredients in blender, blend until combined. Season with salt and pepper to taste.
Assembling the salad
Toss watermelon, cucumbers and feta with the vinaigrette. Garnish with basil and mint. Serve immediately.
Notes
Leftovers don't keep if you dress the salad. If you omit the dressing, the salad should last a couple of days in the refrigerator, but it's best to eat it all when served.