Preheat the oven to 180 C (350 F). Spread the walnuts on a baking tray and bake for 4-5 minutes, until lightly toasted. Transfer the walnuts to a plate to cool, then roughly chop.
Put the dates in a food processor and add the coconut, cocoa powder, chia seeds, vanilla and 1/3 cup of the walnuts. Process until well combined.
Put the remaining chopping walnuts in a bowl. Take a heaped teaspoon of the chocolate mixture and roll it into a ball. Slightly flatten, then gently press the top into the walnuts. Repeat with the remaining mixture.
Put the cookies in a single layer in an airtight container, and chill until firm. The cookies can be refrigerated for up to two weeks.
Each serving provides: 221 kJ 53 kcal 1 g protein 3 g fat (1 g saturated fat) 6 g carbohydrate 1 g fibre 3 mg sodium