Add the oats, walnut butter, chocolate chips, and dates to the bowl of a food processor. Turn the processor on and process until the ingredients have all been chopped up and have formed a crumbly texture. Add the water and process again until the "dough" starts to come together. The dough should be moist enough to hold together but not be "wet".

To form the cookies, press 2 tablespoons of dough into a 1/4 cup measuring cup to mold. You can also just form them by hand.

Press the chopped walnuts into the tops of the cookies. (This is slightly more tedious, but I placed the walnut pieces into the bottom of the measuring cup before pressing the dough on top.) Place cookies on wax paper and refrigerate until solid, about 1 hour.

Cookies taste best the next day and cold but can be enjoyed at room temperature.