Heat oil in a large pan. Add sliced mushrooms and diced onions. Sauté until all the water from the mushrooms is evaporated and the onions are translucent.

Add mushroom and onion soup mix, garlic powder, salt, and pepper. Mix to combine. Pour in boiling water and mix. Let the mixture cook for about three minutes, until the water is absorbed and the mixture is thick. Let cool.

Preheat oven to 175 degrees Celsius (350 degrees Fahrenheit). Line a 9 x 13-inch pan with Gefen Parchment Paper.

On a nonstick surface or silpat mat, lay out puff pastry. Cut into a rectangle, a little shorter than the pan, so it will fit inside. Place half of the filling into the center of the dough. Fold in the edges. Fold up the bottom half, covering the mushroom mixture. Fold over remaining top piece. Gently transfer to the prepared pan. Repeat with next roll.

Using a pastry brush, coat the top of the rolls with beaten egg.

Place on the center rack of oven. Bake for 45 minutes to one hour, or until tops are golden. Serve hot or warm. Enjoy!