Unroll puff pastry sheet onto a large piece of parchment paper. Cut an equal number of 1-inch strips diagonally down both sides of the pastry, leaving the center uncut.
Spread pizza sauce over the center of the pastry. Cover sauce with pepperoni, mushrooms, and mozzarella cheese. Braid strips over the filling, alternating from side to side.
Transfer pastry to a baking sheet. Brush beaten egg white over the top. Sprinkle Parmesan cheese over pastry.
Bake in the preheated oven until puffed and golden, about 25 minutes.
