Prep the pan and oven. Heat the oven to 350°F (175°C).
Grease a 9x5-inch loaf pan and line it with a parchment sling for easy removal.
Grate the zucchini. Use the large holes of a box grater. Lightly squeeze a handful at a time to remove excess liquid, but don’t wring it dry. You want some moisture left.
Mix dry ingredients. In a large bowl, whisk whole-wheat flour, baking powder, baking soda, salt, cinnamon, and nutmeg until evenly combined.
Mix wet ingredients. In a separate bowl, whisk eggs, brown sugar, and granulated sugar (or maple syrup) until smooth.
Add oil, yogurt, and vanilla. Whisk until blended.
Combine gently. Pour wet ingredients into the dry. Stir with a spatula until most streaks disappear.
Fold in the zucchini and any add-ins just until evenly distributed. Do not overmix.
Fill and smooth. Scrape the batter into the loaf pan and smooth the top. If you like, sprinkle with a little turbinado sugar or chopped nuts for a crunchy crust.
Bake. Bake 50–60 minutes, or until the top is set and a toothpick inserted in the center comes out with only a few moist crumbs. If the top browns too quickly, tent loosely with foil.
Cool completely. Let the loaf cool in the pan for 10–15 minutes.
Lift it out and cool on a rack until fully set before slicing. This helps the crumb firm up.
Slice and serve. Use a sharp serrated knife for clean slices. Enjoy plain, or with butter, cream cheese, or a drizzle of honey.