Meanwhile, for the pickled pink onions, put the onions in a small bowl, pour over 350ml/12fl oz boiling water and leave to stand for 10 minutes. Drain and return the onions to the bowl. Add the salt, oregano, cumin seeds, cider vinegar and lime juice. Mix well, then cover with cling film and place in the fridge for 2 hours. The onions will pickle and turn pink.