Serves 4.
1/4 cup red wine vinegar
1 tsp kosher salt
1/4 tsp freshly ground black pepper
1/2 cup extra-virgin olive oil

1 small cucumber, peeled
1/2 small red onion
3 heirloom tomatoes (about 12oz total), cut into bite-sized chunks
3.5 cups watermelon, peeled, seeded and cut into bite-sized chunks
1 red bell pepper, cored, seeded and cut into bite-sized chunks
7 oz feta cheese cut into 1/2 inch cubes
1 cup fresh mint leaves thinly sliced

Whisk the vinegar, salt and pepper in a medium bowl to blend. Gradually whisk in the oil to blend well. Set aside.

Cut the cucumber in half lengthwise, then, using a spoon, scrape out the seeds. Cut the cucumber halves crosswise into thin half-moon slices. Using a mandoline or a sharp knife, cut the onion into 1-inch-long paper-thin slices. Toss the sliced cucumber, onion, tomatoes, watermelon, bell peppers, cheese, and mint in a large bowl with enough vinaigrette to coat. Serve immediately. Refrigerate leftovers.