Cake: Preheat oven to 180 degrees C. Grease a 20x30cm cake tin. Sift together the flour, bicarb soda and cinnamon. Set aside.
In a large bowl combine the sugar and oil until blended. Beat in the eggs one at a time then stir in the vanilla. Stir in the flour mixture just until incorporated. Fold in the pineapple, carrots, coconut and walnuts. Pour batter into prepared cake tin.
Bake in the preheated oven for 45 minutes or until a toothpick inserted into the centre of the cake comes out clean. While still warm, poke holes in the cake with a fork.
Glaze: In a saucepan, combine butter, sugar, buttermilk and vanilla. Bring mixture to a boil over medium heat then reduce heat and cook for 5 minutes.
To Serve: Pour glaze over warm cake then allow to cool completely.