Mix the meat marinade up in a small bowl. Slice the steak against the grain and at an angle into 1cm thick pieces. Place in a sandwich bag with the meat marinade and set aside while you prepare the rest of the ingredients.
Combine the ginger, garlic and scallions in a bowl and set aside.
Prepare the pepper sauce by combining the light soy sauce, Shaoxing wine, sugar, cornflour and black pepper in another bowl and set aside.
Boil the potatoes and once cooled cut them into 2cm slices.
Heat 1 tablespoon oil in a wok or large non-stick saucepan. When it is very hot, add the steak and sizzle for 30 seconds each side. Using tongs, remove the steak from the pan and set aside on a plate. Then, add a dash more oil and wait until it heats up before adding the potatoes. Allow 30 seconds to crisp before flipping them to crisp the other side.
Remove the potatoes from the pan and set aside. Add more oil before adding the peppers and onion. After about 3 minutes, when the vegetables have softened, remove from the pan and transfer to another plate.
Add the remaining oil along with the ginger, garlic and scallions. Stir briefly to cook before adding the pepper sauce ingredients (stir beforehand so the cornflour is mixed in). As soon as it begins to boil and thicken, pour all the cooked ingredients back into the pan to coat.
Serve immediately, topped with the green part of the scallions to garnish.