To make the dressing, put all dressing ingredients into a glass jar and shake until combined. Refrigerate until needed.
Heat a char-grill pan until very hot. Halve nectarines and remove the stone. Brush with olive oil and cook for 5 minutes on each side. Heat a non-stick pan, add a little olive oil and fry the haloumi on both sides until golden. On a large platter form the salad base by arranging the salad leaves and topping with the prosciutto. Add the warm haloumi and nectarines. Sprinkle over croutons. Finish by spooning over the dressing and a sprinkle of olive oil. Serve immediately.