Preheat oven to 400 degrees F. Line a baking sheet with parchment paper or aluminium foil and set aside.
Sprinkle a large cutting board with flour. Unfold thawed puff pastry dough and place on cutting board. Using a rolling pin dusted with flour, roll the puff pastry to a 1/4-inch thick rectangle.
Using a pizza cutter or a knife, trim the dough so that the edges of the rectangle are straight and even. Transfer the sheet of puff pastry to the prepared baking sheet.
Using a sharp knife, being careful not to cut all the way through, lightly score the puff pastry dough 1-inch from the edges, making a rectangle shape within the dough. Using a fork, pierce the puff pastry dough several times within the scored rectangle shape.
In a small bowl, whisk together the whole egg and the water to form an egg wash. Using a pastry brush, brush the edge of the puff pastry with the egg wash.
Bake in preheated 400-degree oven for 15 to 20 minutes, or until the edges of the puff pastry are golden brown and flaky. Serve immediately warm or at room temperature.
Recipe substitutes:
Green onion: ¼ cup diced white or yellow onion can be substituted for the green onion.
Herbs de Provence: Dried Italian seasoning or marjoram can be substituted for the Herbs de Provence.