Wash and prepare all the vegetables and herbs.
Cut the tomatoes into bite-sized pieces.
Slice the cucumbers into rounds or half-moons, depending on their size.
Cut the watermelon into cubes and remove any seeds if necessary.
Thinly slice the red onion.
Cube the feta cheese.
Add the tomatoes, cucumbers, watermelon, onion, olives, feta, basil, and mint to a large serving bowl.
Drizzle with the olive oil.
Season lightly with salt (remember that feta and olives are already salty) and plenty of freshly ground black pepper.
Gently toss everything together just before serving to keep the watermelon and feta from breaking apart.
Serve immediately.