Preheat the oven to 350 degrees F and grease a 9x5-inch pan with nonstick spray.
Add the bananas, zucchini, butter, eggs, and vanilla to a large bowl. Stir to combine.
Stir in the flours, sugar, baking soda, cinnamon and salt. Stir gently to combine fully.
Pour batter into the prepared pan and smooth the top with a spatula so it's even. Bake for 55-60 minutes or until golden brown and a cake tester inserted into the center comes out cleanly.
Cool in the pan for 5 minutes, then remove from pan (carefully) and let cool on a wire rack completely.
Slice and serve.
