Thaw puff pastry according to package directions. On a lightly floured surface, roll out pastry to a 14x11-inch rectangle. Trim to a 12x10-inch rectangle. Place on a parchment-lined baking sheet. Prick pastry with a fork. Build up the sides slightly by folding in about 1/2 inch of pastry on edges. Brush edges with egg white. Crimp or decorate edges with cutouts from pastry trimmings. Brush again with egg white.
In a small mixing bowl stir together flour, granulated sugar, brown sugar, 1 tablespoon ginger, and lemon peel. Cut in margarine or butter until pieces are the size of small peas. Sprinkle half of the ginger mixture over pastry. Arrange pear slices on top, overlapping slightly. Sprinkle with the remaining ginger mixture.
Bake, uncovered, in a 400 degree F oven for 18 to 20 minutes or until pastry is golden and pears are tender. Serve warm. If desired, top each serving with whipped cream and additional crystallized ginger. Makes 8 servings.