01 - Preheat the oven to 350°F. Grease and flour a 9x5-inch loaf pan, tapping out any excess flour.
02 - In a large bowl, whisk together the vegetable oil (or melted butter), eggs, and vanilla extract until smooth. Stir in the mashed bananas and grated zucchini, mixing until evenly incorporated.
03 - In a separate bowl, whisk together the flour, granulated sugar, salt, baking soda, baking powder, and ground cinnamon until well distributed.
04 - Gradually fold the dry ingredient mixture into the wet ingredients using a spatula, stirring just until no dry pockets remain. Avoid overmixing to keep the crumb tender.
05 - Gently fold in the chopped nuts or chocolate chips, if using, distributing them evenly throughout the batter.
06 - Pour the batter into the prepared loaf pan and smooth the top with a spatula for an even surface.
07 - Bake on the center rack for 50 to 60 minutes, or until a toothpick inserted into the center of the loaf comes out clean. Tent loosely with foil if the top browns too quickly during the final 15 minutes.
08 - Let the loaf cool in the pan for 10 minutes, then turn it out onto a wire rack to cool completely before slicing into 10 even portions.