Marinate the bangus
Buy the belly part of deboned milkfish from your local seafood store and cut it into pieces of your desired size. Cut all the calamansi in half with a sharp knife and squeeze the juice out of them into a small bowl. Pour half of the calamansi juice into a large bowl. Also add half of the soy sauce and freshly ground black pepper to the calamansi juice and mix well. Now add the bangus pieces to the bowl and stir so that the fish is completely coated with the marinade. Cover the bowl and allow the bangus to sit in this marinade for at least a couple of hours (overnight is best).
Cook the bangus belly bistek
In a medium sized heavy bottomed pan, shallow fry the marinated bangus pieces. Once the fish is done, remove it from the heat and place on a serving plate. In another pan pour 1/8 cup of canola cooking oil and sauté chopped garlic in it until fragrant. Remove the garlic from the pan and sauté onion slices in the same pan until golden brown. After removing the onion slices from the pan, pour all the marinade from the bowl into the pan. Add bangus and half of the fried onions to the marinade and simmer for 5 to 7 minutes. Garnish the recipe with green chillis and top with the remaining onions and toasted garlic. Your bangus belly bistek is now ready; serve it with garlic rice, or in any other way you prefer.