Cover onions with water and bring to a boil, then drain and peel. Combine onions, caulflower and salt, cover with water and let stand for 18 hours. Drain, rinse well and then drain again. Combine sugar, seeds, pepper flakes and vinegar then bring to a boil and cook until sugar is dissolved. Add vegetables, bring to a boil, reduce heat and cook for 10 minutes or until vegetables are just tender. Pack vegetables in hot sterilized pint jars, cover with hot liquid and seal at once.