Line an 8"x8" baking dish with parchment paper or plastic wrap. In a food processor fitted with an "S" blade, pulse the walnuts until they are finely ground into a meal. Add in the chopped dates, coconut oil and salt, and process again until sticky dough is formed. Set aside 1 cup of this dough to save for the crumble topping, then transfer the rest of the dough to the lined baking dish, using your hands to press it evenly into the bottom of the pan.
To prepare the date filling, combine all of the ingredients in a blender or food processor, and process until a uniform filling is created. Spread the filling over the crust evenly, then crumble the reserved cup of dough over the top. Use your fingers to gently press the crumble topping into the date filling, then place in the fridge to set for 2 hours.
Serve chilled for best texture, and store any leftovers in a sealed container in the fridge for up to a week.