How to Make It
In a small nonreactive saucepan, combine the ketchup, vinegar, sugar, soy sauce and 1/3 cup of cold water. Bring to a boil over moderate heat, stirring. Add the carrot, green pepper and scallions and bring to a boil. Stir the cornstarch mixture, then add it to the pan; stir until the sauce boils and thickens, about 30 seconds. Remove from the heat and cover.
Set a large skillet over high heat for 30 seconds. Add the peanut oil and when a wisp of white smoke appears, add the swordfish steaks and 1 slice of the ginger. Reduce the heat to moderate and cook the fish for 4 minutes. Turn the steaks, add the remaining slice of ginger and cook until the fish is just opaque, about 4 minutes longer. Transfer the swordfish to plates, spoon the sauce on top and serve.