48 hours before you wish to make the dish, begin preparing your salt cod for cooking. Place in a bowl, cover with water and place in the refrigerator. The next day drain, rinse and cover with water again. Place it back in the refrigerator for 10 to 12 hours. Drain, rinse and cover with water again. Refrigerate for another 10 to 12 hours, drain and rinse. Shred the fish and it is ready to use.
Heat the olive oil in a large casserole over medium heat. Once hot, add the onion and cook for 5 minutes, stirring often, until softened and beginning to brown around the edges. Stir in the garlic and cook until fragrant, about a minute. Stir in the tomatoes and roasted red bell peppers, cover partially and cook, stirring from time to time, for 10 minutes, or until the mixture has thickened and darkened in color. It should look somewhat chunky.
Meanwhile, in a separate, medium saucepan, boil the potatoes in salted water for about 10 minutes, until just tender; when you insert the tip of a knife it should go all the way in, but the potatoes should not fall apart. Drain and set aside.
Stir the shredded cod into the tomato mixture. Add the vinegar, parsley, almonds and olives, stir together and continue to cook, partially covered for another 10 to 12 minutes, stirring occasionally and scraping the bottom of the pan, until the ingredients are well amalgamated and the sauce has thickened even more.
Reduce heat to low, stir in the cooked potatoes and the pickled pepperoncini peppers, cover the casserole and simmer for 5 more minutes. The mixture should be very moist and juicy, but not soupy. No need to add salt. Serve with additional pickled pepperoncini, and if you’d like, white rice on the side.