Mashing the pumpkin is definitely the best way to keep the pulp out of the boil kettle, although you'll still end up with a significant amount of break from it. And lautering is going to be slow, even with rice hulls.
What you could have done is toss all the break and trub from the kettle into a large fine mesh hop bag and let it drip out in a colander or strainer or even squeeze/wring it out. Then reboil that recovered wort to sanitize it, chill and add to the fermentor, or make a small batch from it. Done that many times.
A lot of wort is still being trapped in the pumpkin pulp in the mash tun. I ended up with well over a gallon of 3rd drippings after several hours. Made a small batch Saison out of it. Very yummy.
I guess you could squeeze that too, or put a good weight on it.
I roasted 5 cans (75 oz) of pumpkin puree for about 2-3 hours in the oven, spread out over 3 baking sheets in the convection oven. It takes a lot of time since all the water needs to evaporate first before it will roast or caramelize. I ended up with what I estimate to be a good pound of dryish caramelized scrapings that I rehydrated and added to the mash. Although I can taste some pumpkin in the final beer, it's quite subtle, I'm not sure I can detect the roasting effect enough for it being worth the trouble. Next time I'll just add more pumpkin puree (8 or 9 cans total), without roasting.