Preheat oven to 180 C / Gas 4. Grease and flour ring cake tin.
In a medium bowl, sift flour, cocoa, baking powder, bicarb, salt and cinnamon. Set aside.
In a large bowl, cream butter and sugar until fluffy. Add eggs, 2 teaspoons vanilla and milk to the butter mixture. Stir in dry ingredients and mix until well blended. Fold in courgette, orange zest and nuts.
Pour into cake tin. Bake in the preheated oven for 50 to 60 minutes, or until a skewer inserted into centre of cake comes out clean. Allow to cool, then drizzle with glaze.
To make the glaze: In a small bowl mix together icing sugar, orange juice and 1 teaspoon vanilla. Invert cake onto serving dish, then drizzle glaze over.