Oil a 9- by 12-inch baking pan, line the bottom with parchment paper and oil the parchment. Preheat the oven to 350°.
Combine the sugar, oil and molasses in a large mixing bowl. Dissolve the baking soda in a cup of boiling water and stir it into the sugar mixture, then stir in the puréed pumpkin and minced ginger.
In another bowl, sift together the flour, salt, baking powder and all the spices. Stir the dry mixture into the wet. Use a whisk or the low setting of an electric mixer to beat the batter just until everything is combined and there are no lumps.
Pour the batter into the prepared baking pan. Bake for about 45 minutes, or until a toothpick inserted near the center comes out clean.
Allow the gingerbread to cool slightly before cutting.