No cooking, just mix the ingredients together the day before - great with all kinds of Mexican food as a condiment.
Common in Yucatecan kitchens these will keep a good while in the fridge, and are great as a garnish to pep up Mexican food, particularly added to Escabeche, or with a splash of sour cream in a wrap, or on top of beans, or with a salad.Make them a few hours ahead - preferably the day before, to allow the flavours to infuse into the onions.
Approximately 15 calories for a heaped forkful (around 1 tbsp, drained).