Cut the watermelon into 1-inch cubes, removing any seeds you encounter. Spread on a clean kitchen towel and gently pat dry - this prevents the salad from getting watery.

Thinly slice the red onion and soak in cold water for 5 minutes to mellow the bite, then drain. Tear mint leaves with your fingers rather than chopping to prevent bruising.

In a small bowl, whisk together olive oil, red wine vinegar, honey, salt, and pepper until emulsified. Taste and adjust - the dressing should be bright and slightly tangy.

In a large bowl, gently combine watermelon, cucumber, drained red onion, and half the mint. Drizzle with dressing and fold carefully with a rubber spatula to avoid breaking up the feta.

Scatter crumbled feta and remaining mint over the top. Grind a little extra black pepper and serve immediately, or chill for up to 30 minutes.