Preheat your oven to 180°C (160°C for fan assisted ovens) / Gas Mark 4.
Mix The eggs, oil, water and Classic Vanilla Cake Mix gently together and whisk (by hand or electric mixer) for 2-3 minutes until smooth and creamy. Then fold through the bananas, walnuts and cinnamon.
Pour the cake mixture evenly into your two greased cake tins.
Add The cinnamon to the Betty Crocker™ Vanilla Buttercream Style Icing and mix.
Bake in the centre of the oven for 25-30 minutes, or until a skewer inserted into the centre of the cake comes out clean, then cool on a wire rack.
Ice one cake with ½ the buttercream icing. Sandwich together with the other cake and cover the top of the cake with the remaining icing. Using the palette knife gently create swirls on the top.
Decorate with the whole walnuts around in a circle and scatter the chopped walnuts around and about.