Preheat the oven to 180C/350F. Line a 12-count muffin tin with muffin liners and set aside.
In a mixing bowl, combine your cake mix with pumpkin puree and mix well, until a smooth batter remains. Fold through the walnuts, if using them.
Evenly distribute the batter amongst the 12 muffin liners. Bake the muffins for 20 minutes, or until a skewer comes out mostly clean.
Remove the muffins from the oven and let them cool for 10 minutes in the pan, before transferring to a wire rack to cool completely.
* Any 15 oz cake mix can be used. Vanilla or yellow will work well too, but add some cinnamon/nutmeg/ginger to add flavor. ** You can also use 1 can of pumpkin puree (not pumpkin pie filling).TO STORE: Pumpkin muffins will keep at room temperature, covered, for up to three days. If you'd like them to keep longer, store them in the refrigerator and they will keep fresh for up to one week.TO FREEZE: Place leftover muffins in a ziplock bag and store them in the freezer for up to 6 months.