Toast the pine nuts in a dry non-stick frying pan on a medium heat for 1 minute, or until lightly golden, tossing regularly, then remove. Cut off the watermelon rind, pick out any seeds, then slice as finely as you can. Very finely slice the radishes, keeping any nice leaves attached, then gently dress both with 1 tablespoon of extra virgin olive oil and 2 tablespoons of red wine vinegar. Taste and season to perfection with sea salt and black pepper. Arrange the watermelon and radishes on your plates or a sharing platter, sprinkle over the pine nuts, then pick over the mint leaves. Crumble over the feta, and finish with a pinch of pepper from a height.