Preheat oven to 150°C. Line 2 large baking trays with baking paper. Toast the walnuts in a small pan, stirring them frequently until crisp, about 7 minutes. Cool briefly, then chop roughly.
Sift icing sugar, cocoa powder and the cinnamon onto a plate.
Using an electric mixer, beat the egg whites in a large bowl until stiff peaks form. Gently fold cocoa mixture into the egg whites with a metal spoon. Fold in nuts.
Drop the batter in generous teaspoonfuls onto the baking trays, spacing them 2.5 cm apart. Bake for about 20 minutes, or until set. Turn onto a wire rack to cool. Dust with the extra icing sugar just before serving.
Meringues are very sensitive to humidity (they absorb moisture and become sticky), so it's best to bake them on a dry day. Store in an airtight container once they are completely cool. Should you live in a humid climate, seal the cookies in a freezer bag and freeze them.