Combine 1 medium red onion, thinly sliced, and 1½ cups red wine vinegar in a small bowl. Set aside for at least 30 minutes.Pour ¼ cup extra-virgin olive oil into a shallow medium bowl or dish; add 1½ tsp. ancho chile powder, 1½ tsp. dried oregano, ½ tsp. ground cumin, ¼ cup lightly packed fresh cilantro leaves, chopped, and 1 jalapeño, stemmed and chopped and mix well. Add 1 lb. flaky white fish fillets (such as mahi-mahi or cod), cut into 4 pieces; turn fish to coat well on both sides. Marinate for 20 minutes.

Heat a nonstick sauté pan over medium-high heat. Remove the fish from the marinade and place in the hot pan (no need to add more oil or pat fish dry). Season fish with kosher salt. Cook the fish for 4 minutes undisturbed, then turn over and cook for another 2 minutes. Remove the pan from the heat and flake the fish into the pan with a fork, making sure to mix in all the marinade that has stuck to the bottom of the pan. Check for seasoning and add more salt if necessary. Set aside.

Place 4 of 8 fresh corn tortillas on a plate between 2 slightly dampened sheets of paper towel. Microwave on high for 45 seconds. Place warm tortillas in a towel-lined basket or plate and cover. Repeat with the remaining tortillas.

Spoon a heaping spoonful of cooked fish into the center of a tortilla. Top with pickled onions, crema, fresh salsa, hot sauce, and cilantro leaves. Serve with lime wedges for squeezing. Do Ahead: Pickled onions can be made 3 weeks in advance; refrigerate in an air tight container. Fish can be marinated 1 day ahead; refrigerate in an airtight container.

Editor’s note: This recipe for fish tacos first appeared on Epicurious in May 2009. Head this way for more of our favorite Mexican recipes →