Preheat the oven to 200 degrees F. Line a baking sheet with parchment paper. Draw two 4-by-13-inch rectangles about 2 inches apart on the parchment, then flip it over so it is marked-side down.
Make the meringue: Beat the egg whites in a medium bowl with a mixer on medium-high speed until foamy, about 1 minute. Gradually beat in the granulated sugar and continue beating until stiff shiny peaks form, about 6 minutes. Gently fold in the confectioners' sugar with a rubber spatula (do not overmix).
Transfer the meringue to a pastry bag fitted with a 3/4-inch round tip. Using the rectangles as a guide, pipe 4-inch-long lines of meringue side by side in each rectangle. (The lines should touch each other.) Transfer to the oven and bake, rotating the baking sheet occasionally, until the meringue is firm and crisp but not brown, about 2 hours. Remove from the oven and let cool completely on the baking sheet.
Meanwhile, make the lemon curd: Combine the egg yolks, lemon zest, lemon juice and granulated sugar in a medium saucepan; cook over medium heat, whisking, until thickened, about 7 minutes. Whisk in the butter, a few pieces at a time, until incorporated. Transfer the curd to a small bowl, then set in a larger bowl of ice; stir occasionally until the curd is completely cool, then refrigerate until ready to use.
Make the ginger cream: Combine the heavy cream, confectioners' sugar, crystallized ginger and vanilla in a bowl and beat with a mixer on medium-high speed until stiff peaks form, about 5 minutes.
Assemble the napoleon: Place a meringue rectangle on a platter. Spoon the lemon curd on top, leaving a 1/2-inch border. Top with the ginger cream. Place the other meringue rectangle on top and gently press; refrigerate 1 hour. Dust with confectioners' sugar before serving.