Caldeirada is a well known Portuguese dish which, I seem to remember, uses a lot of shellfish. Here is a Goan version.
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 tbs water over the fish. Add salt is desired. Cook on a low heat until fish is half done. Sprinkle turmeric over fish. Add peppers/chillies. Cook until fish is tender.