In a medium bowl, mix the dry ingredients and set aside.
In a larger bowl, mash the bananas, then stir in all the remaining wet ingredients. You can also use a mixer for this step, but your bananas should be ripe enough to mash easily.
Combine the dry ingredients with the wet ones, then mix until homogenous.
Grease a 9x13 casserole dish, then pour in the batter. Spread evenly across the bottom of the dish, then place in the oven to bake for 40-50 minutes.
Once the center of the cake is cooked and the edges are golden, remove and let cool at least one hour before topping with frosting.
Frosting
Add the butter, cream cheese, sugar, and vanilla to a medium bowl.
Mix with a mixer a minute or two until well combined, then taste and explore the texture. If it feels too thin to you, add a 1/4 cup more sugar at a time until you have your desired texture.
Notes
Macronutrients: 71g carb, 19.5g fat, 4g protein
If you prefer like without an excess of zucchini, sub it with one more ripe banana.
This cake keeps well but it fairly perishable, so keep it in the fridge.