In a small bowl, mix the 2 tsp corn starch with the 2 Tbsp rice vinegar.
Add the chicken broth, soy sauce, and ketchup.
Season the fish with 1/2 tsp salt and 1/2 tsp pepper.
Spread the 1/2 cup of corn starch on a wide plate.
Put the eggs in a bowl wide enough to dip the largest pice of cod.
Dredge the fish in the corn starch.
Heat 2 Tbsp of oil in a 12 inch non-stick pan over medium high heat until shimmering.
Move each piece of cod from the corn starch to the egg to coat, then put into the pan.
Cook on the first side for 3 minutes, then turning the fish, until brown on all sides and a little firm to the touch (total cooking time will be about 5 minutes) -- it should NOT be cooked all the way through.
Transfer the fish to a large plate.
Add the remaining 1 Tbsp of oil to the pan, let it warm up, then add the chiles, the white parts of the scallion, and the ginger. Stir fry for 2 ;minutes, until the scallions become translucent, with some brown spots.
Stir the corn starch and vinegar mixture, then pour it into the pan and stir. The sauce should come to a boil and thicken.
Reduce the heat to medium low, return the fish to the pan, and flip it to coat all the pieces uniformly with sauce. Cover the pan, with the lid slightly ajar, and cook for 3-5 minutes, until the fish is cooked fully and starting to flake.
Taste the sauce and re-season with salt and pepper if necessary.
Put the fish on a serving plate (or individual plates) and garnish with the scallion greens.