Preheat the oven to 350 degrees F. Place the butter and sugar in a mixing bowl and beat until light. Beat in the eggs, vanilla and orange zest. Combine the flour, baking powder, salt and ginger in another bowl. Stir into the wet mixture until just combined. Shape the dough into a ball, and then cut into 2. Knead and shape each half on a lightly floured surface into smooth logs, each about a foot long and 2-1/2 inches wide. Place the logs, spacing several inches apart, on a non-stick or parchment-lined baking sheet. Bake 20 minutes, or until a light golden brown. Cool on baking rack 10 minutes. Carefully move the logs to a cutting board and, with a serrated knife, slice, at a slight angle, into 1/2-inch slices. Lay the slices flat on the baking sheet. Return to oven and bake 10 minutes. Turn the slice over and bake 10 minutes more. Cool to room temperature, then store in a tight-sealing container.
Note: Crystallized ginger is available in the bulk food department.