Prepare the FillingIn a medium bowl, mix together the softened cream cheese, Parmesan cheese, onion powder, garlic powder, and black pepper. Add the egg and soy sauce, stirring until smooth. Fold in the well-drained spinach until evenly combined.
Roll Out the Puff PastryLightly flour a clean surface and roll out each puff pastry sheet to approximately 12x10 inches. Cut each sheet into 9 equal squares.
Assemble the ParcelsLay each square in a diamond shape. Spoon a line of the spinach mixture from the top to the bottom corner, leaving about half an inch on each side. Brush the right corner with the additional beaten egg, then fold the left corner over the filling, followed by the egg-washed right corner to seal the parcel.
Bake to PerfectionPreheat the oven to 400°F (200°C). Arrange the parcels on a parchment-lined baking sheet. Brush the tops with the remaining egg wash and sprinkle with extra Parmesan cheese. Bake for about 18 minutes or until golden brown and puffed.
Serve and EnjoyAllow the pastries to cool for at least 10 minutes before serving. Serve warm for the best flavor and texture.