1 medium onion, roughly chopped
1 jalapeño, stemmed and roughly chopped
1 1/2 pounds cod or other thick white-fleshed fish fillet
Salt and freshly ground black pepper
12 6-inch corn tortillas, or 8 12-inch corn or flour tortillas
Fresh salsa
Hot sauce or chili paste (optional)
Sour cream or grated cheese (optional)
Chopped lettuce, tomatoes, cucumber and cilantro sprigs (optional)
Lime wedges

Put onion and jalapeños in nonstick skillet (or microwaveable casserole). Add 1 tablespoon water and the fish; sprinkle with salt and pepper. Cover and place over medium heat (or in microwave). Cook about 6 minutes (3 in microwave), or until the fish is done.

While the fish cooks, heat the tortillas. Toast them in a skillet, one at a time, over medium heat, flipping once or twice until hot, a minute or so. Or heat in a microwave, a half a dozen at a time wrapped in a slightly damp towel, for about a minute.

To serve, put a portion of the fish along with a bit of the onion and jalapeño in a warm tortilla. Top with salsa, hot sauce, cheese or sour cream and vegetables. Squeeze lime juice over all. Repeat with remaining tortillas.