1.Peel and halve the red onion and cut into very fine half-moons and put in a small bowl to steep with the lime juice, to bring out the transparent pinkness in the onions and diminish their rasp. Two limes' worth should do it, but you can find the fruits disappointingly dried up and barren when you cut them in half, in which case add more.
2.Remove the rind and pips from the watermelon, and cut into approximately 4cm / 1½ inch triangular chunks, if that makes sense (arithmetic is not our strong point, and, frankly, as long as they are fair sized chunks that will be fine). Cut the feta into similar sized pieces and put them both into a large, wide shallow bowl. Tear off sprigs of parsley so that it is used like a salad leaf, rather than a garnish, and add to the bowl along with the chopped mint.
3.Tip the now glowingly puce onions, along with their pink juices over the salad in the bowl, add the oil and olives, then using your hands toss the salad very gently so that the feta and melon don't lose their shape. Add a good grinding of black pepper and taste to see whether the dressing needs more lime. Hava Negila! The taste of Tel Aviv sunshine!