Slice the red onion thinly.

Place the sliced red onion in a heatproof bowl.

In a saucepan, bring red wine vinegar and sugar to a boil.

Pour the boiling vinegar mixture over the sliced onion.

Let the pickled red onions cool.

Slice the haloumi cheese thickly.

Oil a grill plate and place over medium-high heat.

Working in batches, grill the haloumi cheese until browned on both sides.

Remove the rind from the watermelon and cut into wedges.

Seed the kalamata olives.

Pick the leaves from the fresh mint sprigs.

Arrange the grilled haloumi cheese and watermelon wedges on a serving platter.

Sprinkle the kalamata olives and fresh mint leaves over the salad.

Arrange the pickled red onions over the top of the salad.

Season the salad to taste with salt and pepper.