Preheat the oven to 350 degrees Fahrenheit.
Grate the zucchini and set aside. There's no need to peel it but if you don't like any green bits in the bread, you are welcome to peel!
In a large mixing bowl, whisk together all wet ingredients but keep the zucchini aside for now.
Whisk in all dry ingredients except for the chopped walnuts or chocolate chips if you're using those. Be sure to spoon and level the flour into the measuring cups and don't scoop straight from the bag.
Fold in the grated zucchini and walnuts and mix until well incorporated. You can also add chocolate chips if you like!
Add to a loaf pan lined with parchment paper. Mine was 8 1/2 x 4 1/2, but 9x5 works too.
Top with additional chopped walnuts and a sprinkle of brown sugar if desired.
Bake for 55-65 minutes or until a toothpick comes out clean. It will rise quite a bit in the oven but will calm down slightly as it cools.
Once done, let cool for at least 1 hour (ideally 2) before slicing. Let it cool right in the pan for about 15 minutes, then carefully lift it out onto a cooling rack to finish cooling.
This part is annoying but it really helps ensure the bread maintains its shape and doesn't completely crumble when you slice!