Preheat the oven to 200 °C (392 °F) and line a baking sheet with parchment paper. Set aside.
Let the frozen scallion pancakes defrost for 2-3 minutes.
Cut the scallion pancakes as shown in the picture below, with the middle piece being a square.
Cut the square-shaped scallion pancake in half to form two rectangles.
In a small bowl, beat the egg. This will be used for brushing the scallion pancakes.
Place one rectangular scallion pancake onto the lined baking sheet and brush a layer of egg wash on it.
Place two half-ovals, pointing toward each other, onto the rectangular piece and brush a layer of egg wash on them. Repeat this layering process once more, brushing a layer of egg wash before adding an extra layer of pancake. One scallion pancake will make one portion.
Flip the pancake over and brush a layer of egg wash on top. Use a knife to make a vertical cut in the middle of the pancake.
Slice the sausage in half vertically and place it in the middle of the pancake, covering the cut. Sprinkle a generous amount of mozzarella cheese.
Repeat the above steps for the second scallion pancake.
Bake for 15-18 minutes. Drizzle with ketchup, and they are ready to serve.