Fish Tacos

Ingredients

• 1/2 red onion, thinly sliced
• About 1 1/2 cups red wine vinegar
• 1/4 cup olive oil
• 1 1/2 teaspoons ancho chile powder
• 1 1/2 teaspoons dried oregano
• 1/2 teaspoon ground cumin
• 1/4 cup lightly packed fresh cilantro leaves, chopped, plus more for garnish
• 1 jalapeño, stemmed and chopped
• 1 pound flaky white fish (such as tilapia, snapper, cod, mahi mahi, or catfish), cut into 4 pieces