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.