First, preheat your oven to 375°F (190°C). While the oven is heating, thoroughly clean your tilapia (linisin nang mabuti ang tilapia) by removing any remaining scales and rinsing it under cold running water. Pat the fish dry using paper towels until no moisture remains.
Using a sharp knife, make three diagonal cuts on each side of the fish, cutting almost to the bone. This will help the seasonings penetrate and ensure even cooking. Season the entire fish, including inside the cavity and the cuts, with salt and pepper (timplahan ng asin at paminta).
Rub two tablespoons of sinigang mix all over the fish and inside the cavity (ipahid ang sinigang mix sa buong isda at sa loob). Let the fish marinate for 10 minutes to allow the flavors to penetrate (palambutin ng sampung minuto).
While the fish is marinating, prepare your stuffing mixture (maghanda ng palaman). In a bowl, combine your diced tomatoes, finely chopped white onions, minced ginger (dinurog na luya), and minced garlic (dinurog na bawang). Add the remaining tablespoon of sinigang mix to the vegetables and season with salt and pepper. Mix everything together until well combined (haluing mabuti).
After marinating, generously stuff the cavity of each fish with your prepared vegetable mixture (punuin ang loob ng isda ng mga gulay). Be careful not to overstuff, as the vegetables will release liquid during cooking. Brush the exterior of the fish with melted butter (pahiran ng tinunaw na mantikilya).
If using banana leaves (dahon ng saging), quickly pass them over an open flame or steam them briefly to make them pliable (painitan ang dahon para lumambot). If using foil, tear off pieces large enough to wrap the fish completely with extra room for folding. Place each fish on its wrapping material and fold to create a secure packet, making sure to double-wrap to prevent any leaks (balutin ng mahigpit upang hindi tumulo ang sabaw).
Place the wrapped fish on a baking sheet and transfer to your preheated oven. Bake for 20-25 minutes at 375°F (190°C). You'll know the fish is done when the wrapper is slightly puffed from steam and the fish flakes easily when tested with a fork in the thickest part. The internal temperature should reach 145°F (63°C).
While the fish is baking, prepare your dipping sauce (gumawa ng sawsawan). Combine calamansi juice (or lemon juice if calamansi isn't available) with soy sauce in a small bowl. If you like it spicy, add thinly sliced Thai chilies.
Once done, remove from the oven and let the fish rest for 5 minutes before unwrapping (pahingang 5 minuto bago buksan). This resting period allows the juices to redistribute throughout the fish. When opening the wrapper, be careful of the hot steam that will escape (mag-ingat sa mainit na singaw).
Serve your pinaputok na tilapia immediately while hot, with steamed rice (mainit na kanin) and your prepared dipping sauce. Pour any juices that have collected in the wrapper over the fish for extra flavor (ibuhos ang sabaw sa ibabaw ng isda).
For storage, any leftover fish can be kept in an airtight container in the refrigerator for up to two days. When reheating, warm it in a preheated 350°F (175°C) oven for 10 minutes, or steam over medium heat for 5-7 minutes until heated through.