How to Make It
Combine watermelon, cucumber, and feta in a large bowl; set aside.
Combine vinegar, shallot, lemon juice, thyme, salt, and pepper in a medium bowl. Slowly drizzle in oil, and whisk until emulsified. Toss watermelon mixture with 1/2 cup of the dressing. Transfer to a serving platter, and drizzle with remaining dressing. Sprinkle with mint leaves before serving.