Place the cubed watermelon and sliced peaches into a large, chilled stainless steel mixing bowl.
In a small glass bowl, whisk together the olive oil, lime juice, honey, salt, and black pepper until the dressing is fully emulsified.
Add the shaved red onion to the fruit mixture.
Drizzle the dressing over the ingredients and use a rubber spatula to gently fold the components, ensuring even coating without compromising the fruit structure.
Add the mint chiffonade and fold once more to distribute.
Transfer the salad to a chilled serving platter and garnish evenly with the crumbled feta cheese.
Serve immediately at a temperature between 40°F and 45°F (4°C - 7°C).