Spicy pickled red onions are a favorite Mexican condiment. They are typically served on tacos of Mexican Slow-Roasted Pork (Cochinita Pibil), where they offer a splash of bright color and fiery piquant flavor. Photo credit: Nicole Shoemaker from Cooking for Keeps.
Place onions in medium heatproof bowl. Add boiling water to cover. Let stand 15 minutes. Drain and rinse with cold water.
Meanwhile, bring remaining ingredients to simmer in small saucepan on medium-high heat. Remove from heat. Let stand 15 minutes. Pour over onions in medium bowl. Cover.
Refrigerate 2 to 3 hours to marinate onions. Drain before serving. Store in covered glass or ceramic container in refrigerator up to 1 week.