Rinse the fish. Pat dry with paper towels. Score both sides and rub with salt and pepper. Sprinkle flour on both sides.
Heat the cooking oil in a wok or frying pan until smoke floats on the surface. Plunge the floured fish into the hot oil. Cook over high heat for five minutes. Flip the fish over and cook for another four minutes. Scoop out and arrange on a serving plate.
Pour off the oil from the wok or frying pan, leaving only about a tablespoonful.
Reheat the oil. Saute the white and light green portions of the scallions, bell pepper and mushrooms with salt and pepper for about half a minute.
In a bowl, stir together the black bean garlic sauce, chili garlic sauce, grated ginger, sugar, tapioca starch and sesame seed oil with 1 and 1/4 cups water. Pour the mixture into the pan. Cook, stirring, until no longer cloudy. Simmer for two to three minutes.
Pour the sauce and vegetables over the fish. Garnish with the dark green portion of the scallions.
Serve the Chinese-style fried fish with black beans and chili sauce at once. Best with rice on the side.