Buy a dressed boneless bangus with the scales, innards, gills and bones removed. Then cut the bangus in half.
Season the fish with salt and pepper buy rubbing it on the meat and the skin.
Combine cornstarch and flour in a deep dish and dredge the fish until fully coated. Set aside.
Heat 1/2 cup of cooking oil in a frying pan and fry the onions for 30 seconds. Remove from oil and set aside.
In the same pan, fry the garlic until brown in medium heat. When brown, remove from pan and set aside.
In the same pan, fry the bangus until golden brown about 5 minutes on each sides in medium heat. When cooked remove from oil and put in a strainer to drain excess oil.
In the same pan, remove the oil and leave only 2 Tbsp. of the used oil. Turn on heat and put soy sauce, calamansi juice, water, oyster sauce and sugar.
Bring the mixture in to a boil until the sugar is dissolved. Then put the onions and fried bangus and simmer for 3 minutes.
Turn off heat and transfer to a serving plate then garnish with fried garlic on top. Serve with steaming cooked rice and enjoy!