For the crust, preheat oven to 350 degrees. In a food processor, combine gingersnaps and sugar; process until finely ground. Add oil and pulse until crumbs are moistened. Transfer mixture to a 9-inch pie plate and press into bottom and up sides. Bake until lightly browned, 8 to 10 minutes. Let cool completely.
For the filling, set a steamer basket in a large saucepan, and fill with 1 inch of water; bring to a boil. Place squash in pan, cover, and steam until tender when pierced with the tip of a paring knife, 12 to 15 minutes. Let cool.
Place squash in food processor and process until very smooth, about 1 minute. Add eggs, brown sugar, half-and-half, fresh ginger, salt, and nutmeg; process until smooth. Place cooled crust on a rimmed baking sheet and pour filling into crust. Bake until set, 35 to 40 minutes. Let cool 1 hour at room temperature, then refrigerate to cool completely, at least 1 hour. Garnish with crystallized ginger.