Preheat oven to 350 and spray a 12"x17" sheet pan with non-stick cooking spray.
In bowl beat your butter and sugar for a few minutes until light and fluffy.
Add in your bananas and continue to beat until combined.
Add in your eggs and vanilla and beat again.
Fold in your zucchini until incorporated.
In another bowl whisk together your flour, baking soda, salt and cinnamon.
Add your flour mixture into your wet mixture and beat until combined.
Add in your milk and beat until just mixed.
Pour into your prepared pan and bake for about 25 minutes or until golden.
Remove from oven and let cool completely.
Meanwhile to make your frosting, in bowl beat your butter until fluffy.
Add in your cream cheese and mix together.
Beat in your salt, cinnamon and vanilla until combined.
Slowly add in your powdered sugar until you reach your desired consistency.
Spread your frosting over your cake and cut and serve.