Method:
Preheat oven to 350°F. Grease an (8-inch) square baking pan with oil and set aside.
In a large bowl, whisk together flour, cocoa powder, pumpkin pie spice, baking powder, baking soda and salt. In a separate bowl, whisk together oil, sugar, eggs, pumpkin and vanilla. Whisk flour mixture into pumpkin mixture until well combined then transfer batter to prepared pan.
Bake until the cakes pulls away from the sides of the pan and a toothpick inserted in the center comes out clean, 40 to 50 minutes. Set aside to let cool then cut into squares and dust with powdered sugar, if you like.