How to Make It
In a medium heatproof bowl, toss the onions with 1 tablespoon of salt and let stand for 5 minutes. Add the boiling water and let stand for 10 minutes longer. Pour the onions into a colander, rinse under cold water and drain well; pat dry.
Wipe out the bowl with paper towels and return the onions to it. Stir in the tomato, chiles, lime juice and cilantro and season with salt and pepper. Cover with plastic wrap and refrigerate overnight. Serve at room temperature.