Before starting, gather all your ingredients and equipment. You'll need a large whole fish like tilapia or lapu-lapu, salt, cooking oil, white vinegar, sugar, red bell peppers, red onions, garlic, and whole peppercorns.
Clean your fish thoroughly, removing all scales and innards. Make 3-4 diagonal cuts on each side of the fish, about half an inch deep. Rub salt all over the fish, making sure to get some into the cuts and cavity. Let the fish rest for 10 minutes to reduce fishiness.
Heat half a cup of cooking oil in a large pan over medium-high heat. When the oil is hot (you can test by dropping a tiny piece of bread – it should sizzle immediately), carefully put the fish in. Fry each side for 7-8 minutes until golden brown and crispy. Remove the fish and place on paper towels to drain excess oil.
In a clean pan, pour one cup of white vinegar and turn the heat to medium. Let it come to a boil. Add quarter cup of sugar and stir until it dissolves completely. Add your crushed garlic and whole peppercorns. Let these cook for 1 minute until you can smell the garlic.
Add your sliced red onions and bell peppers to the pan. Cook them for 2-3 minutes until they're slightly soft but still crispy. Add half a teaspoon of salt and stir everything together.
Carefully place your fried fish into the pan with the sauce. Gently spoon some of the hot sauce over the fish. Let everything cook together for 2-3 minutes. Turn off the heat and let it rest for 5 minutes.
Transfer everything to a serving plate, making sure to pour all the sauce and vegetables over the fish. For the best flavor, let it sit for 15 minutes before serving. You can serve this hot or at room temperature, always with plenty of steaming white rice.
Remember: Don't throw away the sauce! It's perfect for pouring over your rice. Store any leftovers in the refrigerator and enjoy within 3 days. The flavor actually gets better the next day.