In a pan on medium heat, roast the pepitas for xx minutes until puffed. Stay with them, they can go from perfect to burnt in a second.
Let cool completely.
In a pot add the brown sugar and let dissolve. Do not stir. Swirl the pot. Once the sugar is dissolved and it is bubbling about xx minutes, add the pepitas (the temperature will go down temporarily) and continue cooking, constantly stirring with a rubber spatula until it's bubbling again.
Immediately remove the mixture from the heat and stir in the pumpkin spice.
Pour the candy mixture out onto parchment paper. Stretch or spread gently with a silicone spatula if necessary. The candy will set and harden in about 30 minutes.
Break the brittle up into smaller pieces.