Remove the stems from the pumpkins, cut a 1-inch hole around their top and scoop out the seeds. Pour one tablespoon of oil into each pumpkin cavity, season well with salt, then place each pumpkin upright on a sheet pan and roast for 25 minutes, or until the flesh is tender.
Let cool completely, then carefully scrape out the flesh, leaving the pumpkin shells intact to be used as serving vessels.
Scoop the flesh of the avocados out of the rind and into a bowl. Mash the avocados with a fork, making sure to leave plenty of chunks. Mix in the remaining ingredients plus the cooled, cooked pumpkin and salt.
Fill pumpkin shells with guacamole and serve with corn tortillas chips.