Roast half of the onion slices in a large saucepan until golden. Place the pieces of fish on top, the tomatoes, the rest of the onions, the garlic, the parsley, season with salt and pepper, pour on the oil, the wine and a little water and let everything cook very slowly until the fish is done.
The polenta is now being prepared. When the water starts to boil, add salt and slowly stir in the corn grits, cooking time approx. 40 minutes.
Arrange the soft polenta in a shallow bowl, place pieces of fish on top and pour the soup-like sauce over it.