Preheat oven to 350 degrees F and set oven racks to upper-middle and lower-middle racks. Butter two 8.5 by 4.5 inch loaf pans.
Cream butter and sugar in a large bowl until light and fluffy and the butter is visibly lighter in color. Add eggs, one at a time, until well incorporated.
Stir together dry ingredients with a whisk to make sure they’re fully combined, including the flour, cocoa powder, baking powder, baking soda, salt, cinnamon and nutmeg.
In a medium bowl, combine the buttermilk, oil, yogurt, vanilla and zucchini.
Stir in 1/3 of the dry ingredients into the butter/sugar mixture, followed by ½ of the zucchini mixture, another 1/3 of the dry ingredients, the remaining zucchini mixture, and finally, the last of the dry ingredients, stopping to scrape the sides of the bowl between each addition. Try not to overmix.
Gently stir in the chocolate chips.
Pour into prepared loaf pans as evenly as possible. Place on loaf on the upper-middle rack and the other on the lower-middle rack. Bake for 55-65 minutes, rotating loaves from bottom to top and top to bottom halfway through bake time.
Remove from oven and place on cooling rack. Cool for 5 minutes before running a knife around the sides of the pan and removing to the cooling rack to cool completely. Slice with a serrated knife.
Store this bread at room temperature for 2-3 days or refrigerated for up to 5 days. It freezes beautifully. Just wrap it in foil and place in a re-sealable bag. Thaw at room temperature overnight or pop in the oven for 10-15 minutes to melt the chocolate chips.