Begin by preparing the fruit. Chop up the watermelon into 1-inch cubes and place into a large bowl or trifle. Rinse and dry the blueberries and add to the watermelon. Peel and core your apple, chop into small cubes or pieces (about 1/2 inch).
Add chopped fresh mint.
In a small bowl, whisk together lemon juice, red wine vinegar, and honey.
Pour over top of the salad, and toss together to make sure the fruit is evenly coated. Top with feta to serve
Notes
Salad can be made up to 8 hours ahead. Feta and mint should be added later (less than 2 hours before serving).