Goa, located on the west coast of India, has a regional cuisine known for seafood and coconut milk. But there's another ingredient in the Goan pantry that calls back to its Portuguese colonial roots: vinegar. That's what gives the slight tang to this easy, not-too-spicy fish stew. Like many curries, the flavor improves the next day, so I suggest making the base for the sauce the night before, even freezing it, and reheating it when you're ready for dinner. Once the sauce is simmering, cooking the fish and getting dinner on the table takes just a few minutes.