Cook the canned pumpkin over a low simmer until reduced to about a 1/2 cup, about 20 minutes or more. The pumpkin should be steaming and bubbling lightly as you gently heat it to evaporate some of the water to condense it, stir it occasionally. Cool.
Cream the shortening and the sugars in a mixer until creamy. Beat in vanilla and the cooled pumpkin. Sprinkle in the flours, guar gum, cinnamon, and salt. Beat until well blended. You mix in any additional add in's at this point if desired.
The dough should be very stiff and dry feeling. You should be able to easily pick up a chunk and gently roll it into a ball without it sticking to your hands. If you need to, add in some more flour to make this happen, 2 tablespoons at a time, any of the flours from above will do!
Place golf-ball size balls of dough on a parchment lined cookie sheet. Use your hand to gently press the tops down slightly, these do not rise or fall much! Bake in a 350 degree oven for 12 minutes until turning just golden around the edges. You want to just lightly under-bake these, and let them cool and set out of the oven to keep the texture perfect!
If you'd like to top with icing when the cookies are cooled, mix powdered sugar with melted margarine. Add just enough milk (1-3 teaspoons) of any variety non-dairy milk to make a thick icing to dollop on top of the cookies. It should not be so thin it drips: it should stay put when placed on top of the cookie!