Roll the stromboli seam side down and carefully reposition it diagonally on the baking sheet, making sure the seam remains on the bottom.

Brush the top and sides with beaten egg and sprinkle evenly with Parmesan.

Using a sharp paring knife, cut 5 or 6 shallow diagonal slashes, evenly spaced, into the top so the filling is visible.

Bake until well browned and some of the cheese is bubbling through the slashes, 25 to 30 minutes.

Using a wide metal spatula, transfer the stromboli to a cutting board and cool for 15 minutes.