Preheat oven to 375 degrees
Prepare an 18x13-inch half sheet pan. Grease pan lightly with shortening. LIne with parchment paper and grease and flour paper. Set aside.
Using a mixer, combine pumpkin, eggs, and sugar. Beat until combined.
In a separate bowl, stir together flour, baking soda, salt, cinnamon, ginger, and nutmeg. Add to pumpkin mixture. Beat just to combine. Pour into prepared pan and spread evenly.
Bake in preheated oven 15-18 minutes or until cake is firm and springs back when touched.
While cake is cooking, cut a piece of parchment paper slightly larger than pan and dust with powdered sugar. While cake is still hot, turn out onto paper and, from the short side, immediately roll up in the paper. Allow to cool.