Here's a quick and simple stovetop recipe for cod fillet.
Put oil or your preferred fat to cover the bottom of a medium saucepan with a lid.
Chop an onion toss it in and over medium heat until golden.
Cut potato into slabs about half inch thick to cover the pan.
Add salt pepper spuds and enough water to nearly cover the spuds.
Cover and simmer for about ten minutes.
Place your cod fillet on top of the potatoes, cover again for 5-10 minutes until potatoes break with a fork and fish is done.
Serve in a bowl, the liquor and all is delicious.
I love this recipe, but beware the russet potato - tried to make this with russets once and the dang things melted and burned to the bottom.
Just thinking, this simple recipe would also be great to tweak with additions like guajillo..