Bring 2 litre of water to the boil in a saucepan, then add 2 teaspoons of salt and the onions. Bring back to the boil and boil a few seconds, until the onions have softened slightly and the red color has bled into the white. Drain, and tur n the slices into a bowl. Coarsely grind the peppercorns and cumin, and fold into the onions along with th e rest of the ingredients. Add just enough cold water barely to cover the onions , and fold all together. Let stand for at least 4 hours -or longer, until they take on a beautiful pink color.