Peel the onions and slice them as thin as you possibly can.

Transfer them to a medium-sized bowl.

Pour the boiling water into the bowl, and let the onions soak in the boiling water for 5 minutes.

Drain thoroughly in a colander. While the onions sit
in the colander, combine the marinade ingredients
in the same bowl, Mix well. Stir in the onions, and let them sit in the marinade for 10 - 15 minutes.

Transfer the onions with all the liquid to a jar with a tight-fitting lid, and chill until very cold.

These keep for months in the refrigerator.