This quick and easy recipe uses salted soy beans, or tauchu, as the main flavor component. If you missed my post on Nyonya Chicken Stew (Pongteh), they both use the same main ingredient which lends a smoky and earthy flavor to meats. Caramelized onions are added to further accentuate the flavor.
You can find salted soybeans in local Asian grocery stores. Since it is salty on its own there is no need to add more salt to the dish and sugar is added instead to balance out the taste. The fish is pan-fried beforehand to give it some form and prevent it from breaking down during the simmering stage.