In the bowl of a food processor combine the avocado and melted butter and pulse until very smooth and there is no lumps of avocado left.
Add the vanilla, cocoa powder and 3 c. of powdered sugar and pulse until mixture comes together to form a ball. Fold in the chopped nuts. (or mix in using your hands)
Line a sheet pan or cookie sheet with wax paper. Using your hands roll the chocolate mixture into little 3/4 inch balls and arrange on cookie sheet. (If the mixture gets too soft put it into the refrigerator or freezer to harden a little)
Place the cookie sheet of chocolate balls into the refrigerator until firm.
Once the truffles have hardened roll them in extra powdered sugar and store in a covered container in the refrigerator.