Preheat oven to 350°F. Thoroughly grease a 9x13” cake pan with cooking spray, olive oil, or butter.
In a large bowl, microwave 1/2 cup (1 stick) butter in 20 second intervals until melted, about 45 seconds total. Stir in 3/4 to 1 cup of maple syrup, depending on how sweet you like things. 1 cup will not make it overly sweet, but it will be pretty cake-sweetness-level. I like it with 1 cup.
Add 3 bananas to the bowl and mash very very well. We don’t want big chunks. Stir in 1 grated zucchini, 2 large eggs, and 2 teaspoons vanilla extract until smooth.
Pour 2 cups all-purpose flour on top of the batter - DON’T MIX IT IN YET! Pour 1/2 cup cocoa powder, 1 teaspoon baking soda, 1/2 teaspoon baking powder, 1/2 teaspoon cinnamon and 1/4 teaspoon salt on top of the flour and use your fingers or a fork to thoroughly mix all of the dry ingredients together before mixing them into the wet ingredients.
Mix the dry ingredients into the wet ingredients, and stop mixing as soon as they are combined. Over-mixing will lead to tough baked goods!
Pour batter into the cake pan. Sprinkle the chocolate chips and flaky sea salt over top.
Bake for 25 to 30 minutes, until a toothpick or paring knife inserted into the center of the pan comes out clean.
Allow to cool slightly, then slice and enjoy!
Store covered with plastic wrap, at room temperature.