Preheat your oven to 350 degrees F. Grease a 9-inch x 13-inch baking dish and set it aside.
In a large bowl, whisk together the angel food cake mix and pumpkin pie spice. Then stir in the pumpkin puree until well combined. Pour the cake batter into the prepared baking dish and spread evenly.
Bake for 25-30 minutes, or until the edges of the cake are slightly golden brown and the centers springs back to the touch.
Remove from the oven and allow to cool completely on a wire rack. (If the cake isn't cooled all the way, the frosting will melt.)
Frosting
Using a stand mixer or hand mixer, beat together the butter and cream cheese until well combined and fluffy, about 2 minutes. Mix in the vanilla. Beat in the powdered sugared 1/2 cup at a time before adding the cinnamon. Continue to beat until everything is well incorporated and the frosting is fluffy, about 2-3 minutes.
Once the cake has cooled completely, you can cut it into 12 slices and pipe the frosting onto each slice, or simply spread the frosting over the entire cake before cutting.
Notes
Cover and refrigerate any leftovers for up to 3 days.