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 mahi mahi or cod), cut into 4 pieces
Salt
8 fresh corn tortillas
Mexican crema, homemade or store-bought
Fresh Tomato Salsa
2 limes, cut into quarters