Preheat the oven to 325ºF. Butter and line a loaf pan with parchment paper.
Beat together the melted butter and brown sugar. Add in the eggs one at a time. Mix in vanilla and milk until combined.
Fold in the shredded zucchini.
Sift the flour, baking soda, baking powder, salt, and cinnamon into the bowl. Fold to just barely combine.
Fold in 1 cup of the chocolate chips until no dry spots remain. Do not overmix.
Pour the batter into your prepared loaf pan. Sprinkle the remaining ¼ cup of chocolate chips on top.
Bake for 60 to 75 minutes, depending on your pan. See notes. Check for doneness by inserting a toothpick in the center.
Allow to cool in the pan until safe to touch. Remove to a cooling rack to cool completely before serving (if you have the self-control... otherwise, enjoy a nice warm slice with gooey melted chocolate).
Notes
NOTE: This loaf takes 1 hour in a dark metal/non-stick pan. If you use a glass pan, it will take closer to 1 hour 15 minutes. Rely on a toothpick inserted in the center to check for doneness and continue baking in 5 minute increments until the toothpick comes out clean.