Preheat oven to 350°F. Line a loaf pan with parchment paper or heavily grease the bottom and sides with butter or oil.
In a large bowl, stir together oil, sugars, eggs, mashed bananas, grated zucchini, sour cream, and vanilla. Mix until well combined.
In a small separate bowl, combine flour, baking soda, cinnamon, and salt. Add large spoonfuls of the dry ingredients to the wet and stir just enough to fully incorporate all of the ingredients. Fold in the walnuts and chocolate chips (if using).
Pour batter into the prepared pan. Cook in the preheated oven for about 60 minutes or until a toothpick inserted into the middle comes out clean. You can also utilize an instant-read thermometer inserted into the center and bake your banana bread until it reaches an internal temperature of 200 to 205°F, as this method guarantees optimal doneness without the risk of overcooking.
When done, immediately set the pan on a cooling rack. Once it is cool enough to handle, remove the loaf from the pan and parchment paper (if using) to allow it to fully cool on the rack.
Notes
zucchini note - be sure to pack grated zucchini into measuring cup to measure. For best results, squeeze as much moisture out of the zucchini as possible. You can do this by pressing it through a fine mesh sieve or squeezing it tightly inside a clean kitchen towel.Recipe makes 1 standard sized loaf.You may use two mini loaf pans in place of a single standard size loaf pan if you wish. Cooking time will be reduced, so remove from oven when center is cooked.If you have a lot of ripe bananas, you may want to double or triple this recipe.This banana bread freezes well. Just slice, wrap tightly with plastic wrap, and freeze until ready to eat. For longer storage you may also want to use freezer paper to keep it from getting freezer burn.Nutritional information is based on the loaf getting cut into 12 pieces and includes the chocolate chips.