1 large onion, sliced thick
Cilantro and Mexican oregano, dried, crumbled
Salt and pepper
Bread slices, buttered
Vinegar and water, in equal amounts
Cayenne pepper, to taste
Put onion slices in a bowl. Coat with spices, then cover with water and vinegar mixture. Refrigerate for 8 to 10 hours.
Drain onion slices, season with salt, pepper and cayenne. Place between two slices of buttered bread.