Preheat the oven to 350°F.
Brush a standard size muffin pan with melted butter, spray with baking spray, or line with cupcake liners. Set aside.
Wash and trim the zucchini. Shred using a box grater or chop into smaller pieces and shred in a food processor. Set aside.
Add buttermilk, eggs, oil and vanilla extract to a large mixing bowl and beat until smooth. Add brown sugar and mix until sugar is well incorporated. Add the shredded zucchini and stir to distribute evenly.
Sift flour, baking soda, baking powder, and cinnamon into a small mixing bowl. Stir in the kosher salt. Add the flour mixture to the liquid mixture and mix until just combined.
Fold in the chocolate chips. Optional: reserve a handful of chocolate chips to sprinkle on top of the batter before baking.
Transfer the batter to the prepared muffin pan, fill it all the way to the top, sprinkle the reserved chocolate chips on top if using, and bake for 17 - 19 minutes until a toothpick inserted in the center of the muffin comes out clean with just a few crumbs attached.
Allow the muffins to cool in the pan for 10 minutes before removing them from the pan and let cool further on a wire rack.