Clean the fish and cut several cuts on the thick part of the fish meat. Drain completely. Coat the fish with a thin layer of cornstarch.
Marinate with a small pinch of salt and 3-4 slices of ginger. Set aside for 10 minutes.
Heat around 3 tablespoons of cooking oil in a pan and fry the fish until crispy on both sides. Place on side down and let the fish stay for 3-4 minutes over slow to middle fire. Then turn over and fry the other side.
Move the fish to one side of the pan and fry scallion until aromatic. Place black bean sauce, water or stock in. Simmer for 3-4 minutes and slightly turn up the fire until the sauce is almost thickened.
Add sections of 2 scallions and then heat around 2 tablespoons of hot oil. Pour the hot oil over the scallions.