Rinse, drain and peel ginger; Slice a small part of the ginger; Grate the remaining with a microplane grater over a bowl.
Put a strainer over a bowl; Line the strainer with a piece of cheesecloth, draping the corners over the sides; Spoon the grated ginger into the center of the cheesecloth; Gather up the 4 corners and twist to squeeze the grated ginger for juice for later use.
Rinse and drain spring onion; Cut off any roots; Chop it finely.
Insert a knife into the anus near the tail of a pomfret; Draw the knife toward the head, splitting the fish to the base of the gills; Spread the abdominal cavity with fingers; Reach in and pull out the entrails; Rinse the cavity under running water; Cut off the head with the knife; Rinse the fish under running water again; Pat-dry the fish with kitchen paper.
Lay the pomfret horizontally on the cutting board with the back of the fish facing you; Position a filleting knife behind the gills and cut downward at a slightly diagonal through the bone to cut off the head; Place the knife down where the tail meets the body and cut straight down through the skin and the bone of the fish to cut off the tail.
Insert the knife behind the gill cover of the pomfret and cut downward till the knife hits the backbone; Turn the knife so that it is aligned with the ribcage and push it down so that the tip extends about midway down the fish’s body; Run the knife along the ribcage to separate the meat from the ribs; Pull the meat away from the ribcage (repeat the step for anther side).
While holding a piece of fillet steady on a plate with on hand, remove any tiny pin bones with a needle-nosed pliers; Slice the flesh thickly (repeat the step for the other fillet; there should be 8 slices in total).
Add seasoning (1), the ginger juice and the spring onion into a mixing bowl; Mix; Marinate the fish slices with it the seasoning mixture for 15 minutes.
Add 6 tbsp cornstarch into a flat plate; Coat each fish slice with the cornstarch evenly.
Add 6 tbsp oil into a wok; Heat over a high heat; Turn to a low heat; Arrange the fish slices into the wok; Pan-fry them over a low heat till both sides are golden brown; Set the fish slices aside; Turn off the heat; Pat-dry the fish slices with kitchen paper.
Add seasoning (3) into a mixing bowl; Mix.
Set the oil in the wok aside, leaving 1 tbsp oil in the wok; Heat it over a high heat; Add the seasoning (3); Bring to the boil over a high heat; Return the fish to the wok; Stir-fry it over a high heat till the sauce dried out; Turn off the heat; Arrange it on a serving plate; Ready to serve.