Not a completely new idea. Plenty to see if you search the internet. But all of those are done in lasers with large Z depth beds. Have to get a little more creative with the Forge.
I sadly have no more pumpkins available, so this won’t be a guide with images, or even with the certainty of having tested the concept. But pumpkins are pretty simple, so I don’t feel a test is really required.
Prepare the Pumpkin:
Pumpkin selection: You want to find one with a large flat side. Typically this is not challenging to do at a grocery store. Aim for low-budget pumpkin suppliers who just grow a giant patch, not the high budget or family garden places that carefully tend the crop making sure to get as round as possible.
You are going to cut out the large flat side, so that you get something which will fit inside the Forge. Do this much like you normally cut the top of the pumpkin (and because you are doing this you don’t need to cut the top). Going with a bit of an angle may help, but is not strictly required (gravity won’t be pushing this in after all).
Once you have cut out a large chunk of reasonably flat pumpkin face, you want to hack off the meat from the back of that face to get yourself thin enough to fit in the Forge. But leave some depth to your final face if you want to raster engrave. You can go really thin if you just want to cut things away.
With the large chunk of meat, cut out the middle section (all space where you will have your carved design. You should think in terms of making a picture frame. Take this pumpkin meat frame, and use toothpicks to re-attach it to the inside of the pumpkin (after gut removal and possibly candle insertion). You will later use toothpicks to attach your carved face back to the frame so it rests inside your pumpkin once more.
Notes about cutting
First, you will have to figure out the right settings for the laser. If you plan to just cut, then it depends completely on how thick of a piece you made. But you can get away with just going slow and powerful, since a cut is a cut. Extra energy is wasteful, but not strictly harmful. But if you want to engrave, then you need to find the right power settings. So, get two pumpkins. Or cut a chunk off the back side to play with. Or very slowly raise power applied until you finally engrave.
The smell… is terrible. Hopefully the filters of the Forge are amazing, but most likely you will get some smell.
There will be black residue all over the pumpkin where the laser burnt it. Leave this for effect, or just wipe it off with a damp cloth.