
Preheat oven to 375 F.
Rinse tilapia well, rinsing cavity well. Pat dry. Make two or three slits across the body of the fish on both sides.
Rub both fish all over, including the cavity, with 2 tablespoons of the tamarind base powder. Let stand for about 10 minutes.
In a bowl, combine tomatoes, onions, ginger, garlic, the remaining 1 tablespoon of tamarind powder, and salt and pepper to taste. Stir to distribute.
Stuff each fish's cavity with tomato-onion mixture.
Liberally brush the outside of both fish with butter and Individually wrap in aluminum foil, Double wrap to prevent juices from leaking.
Place fish packets on a baking sheet. Bake in the oven for about 20 to 25 minutes or until fish is cooked through.
Serve hot with dipping sauce.
Combine calamansi juice and soy sauce to taste.