While I have never made a Pumpkin Beer, I spoke with my local brewmaster last year who told me he cuts up a whole deseeded pumpkin into 3” chunks, places them on a roasting pan, seasons them with pumpkin spice and roasts them in the oven at 325° for about an hour to concentrate and meld the flavors. Then he adds the chunks to the top of the mash along with rice hulls.
For what it’s worth, he makes the best Pumpkin Ale I’ve ever had the pleasure of drinking.