If your dates still have pits, make a shallow slice down the middle of each date (be careful not to slice all the way through) and remove the pit. Gently open each date to make space for the filling.
In a small bowl, combine the chopped pistachios, chopped walnuts, honey (or syrup), cinnamon, and vanilla extract. Mix until the nuts are well coated.
Spoon the nut mixture into the center of each date. Enjoy!