Whisk in the tomato sauce and kosher salt. When the mixture starts to boil, add the fish pieces, spooning the sauce on top to cover them. Bring back to a gentle boil.
Cover (use heavy-duty foil if your skillet does not come with a lid), lower the heat to medium-low, and cook until the fish is cooked through, for about 15 minutes.
Garnish with parsley and serve.
2 tablespoons parsley
Video
Notes
Seasonings, especially salt, are guidelines. Adjust to taste.
While you can make this recipe with regular canned tomato sauce, I prefer to use strained tomatoes by one of two Italian brands - Pomi or Bionature. These tomatoes are smooth, flavorful, and sweet. A domestic US tomato sauce will be more acidic.
You can use frozen fish, but not so frozen that you can't cut them into chunks. I like using partially frozen fish because it makes cutting them easier. So, I defrost them the night before in the fridge, and by the time I'm ready to use them, they're just a bit frozen. Remember that after adding frozen fish, the stew will take slightly longer to return to a boil.
You can keep the leftovers in an airtight container in the fridge for up to 3 days. Reheat them gently, covered (to prevent splatters), in the microwave at 50% power.