Caldeirada is a well known Portuguese dish which, I seem to remember,
uses a lot of shellfish. Here is a Goan version.

Ingredients
10 large mackerel or sardines, cleaned and head removed
4 large onions, sliced
2 large tomatoes, sliced
1 head of garlic, finely sliced
1 inch piece of ginger, finely sliced
3 tbls light oil
1 Tsp vinegar
1/4 tsp ground turmeric
4 bell peppers (red/green) and or green chilies
salt to taste

Method
Layer a few slices of onion and tomato in a pan. Place
1/2 the fish over onions an tomato. Add another layer of
onion/tomato and then another layer of fish. Sprinkle with the garlic and
ginger. Scatter over the remaining onion and tomato. Pour the oil, vinegar
and about 6-7 Tsp water over the fish. add salt is desired. Cook on a
low heat until fish is half done. Sprinkle turmeric over fish. Add peppers/chilies.

Cook until fish is tender.