Ensure that all the seeds have been removed from the watermelon chunks.
Slice the onions into thin vertical half moons.
Chop or tear half the mint leaves into small pieces, leaving a few leaves whole for garnishing.
Put the watermelon, onion and torn mint leaves in a bowl.
Make a dressing with olive oil, a pinch of salt, cracked pepper, vinegar or lime juice and pour onto the melon and onions. Let stand for at least 15 minutes.
Before serving, sprinkle crumbled feta cheese and the remaining mint leaves.
Since feta is salty only a pinch of salt is required earlier for the dressing.