In a bowl, season fish fillet with salt and ½ teaspoon of ground black pepper.
Heat oil in a pan. Then, roll the fish fillet onto the flour.
Now, fry the fish fillet until golden brown. Set aside.
Heat oil in a pot, saute garlic until golden brown. Then, add onion, ginger, and tomato. Mix until softened.
Toss in fermented black beans and season it with soy sauce and ground black pepper. Mix it again.
Then, pour in the water, vinegar, and sugar. Brint it to boil.
Now, add the fish fillet and pour the diluted corn starch into the pot. Simmer.
Transfer onto a serving plate, and top it with young onion.
Serve hot and enjoy!