Preheat the oven at 200 °C or 392 °F. Line the baking sheet with parchment paper. Set aside.
Let the frozen scallion pancakes defrost for 2-3 minutes.
Cut the scallion pancakes like the picture below. The middle piece should be a square.
Cut the square-shaped scallion pancakes into half (two rectangles).
In a small bowl, beat the egg. It will be used to brush on the scallion pancakes.
Place a rectangular scallion pancake onto the lined baking sheet. Brush a layer of egg wash on it.
Place two half ovals, pointing each other, onto the rectangular piece. Brush a layer of egg wash on it. Repeat steps 6 and 7 once again. You must brush a layer of egg wash before adding an extra layer of pancake. One scallion pancake can make one portion.
Flip the pancake over and brush a layer of egg wash on top. Use a knife and make a verticle cut in the middle of the pancake.
Slice the sausage in half, vertically. 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 one.
Bake for 15-18 minutes. Drizzle with ketchup, and they are ready to serve.