Start by cutting the watermelon into bite-sized cubes, ensuring they are juicy and vibrant. Slice the peaches thinly, discarding the pits. In a large mixing bowl, combine the cubed watermelon and sliced peaches, gently mixing them.

Thinly slice the red onion and add it to the bowl with the fruit mixture, distributing it evenly.

Chop the mint leaves finely and sprinkle them over the fruit and onion mixture, gently tossing to combine.

Crumble the feta cheese over the fruit mixture, ensuring small pieces for even distribution.

In a small bowl, whisk together the olive oil, balsamic vinegar, salt, and pepper until well combined.

Drizzle the dressing over the salad and gently toss everything together. Serve immediately or refrigerate for about 30 minutes.