Place the pumpkin pie spice and powdered sugar in a medium bowl and whisk to combine; set aside.
Place the cream cheese and butter in the bowl of a stand mixer fitted with a paddle attachment and beat on medium speed until fully combined and smooth, about 1 minute.
Reduce the speed to low, slowly add the powdered sugar mixture, and beat until fully incorporated and smooth, about 3 minutes. Stop the mixer and scrape down the paddle and sides of the bowl with a rubber spatula.
Turn the mixer to medium speed, add the pumpkin, and mix until fully incorporated and smooth, about 1 minute. Use immediately. I pipe mine on - but whatever works best for you is fine.