Place sliced red onion in a colander. Rinse thoroughly with cold water; let drain. This will help reduce the overpowering “bite” of the onion while still letting the flavor shine through.

In a large bowl, add the drained red onion, watermelon, cucumber, cheese, and mint. Top with the olive oil, lemon juice, and a splash of red wine vinegar. Add a pinch of salt and several grinds of fresh black pepper.

Stir to combine; taste and add additional salt, pepper, olive oil, or vinegar as desired.

Serve immediately.