Whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
In a separate bowl, combine all of your wet ingredients, adding the zucchini last.
Add the wet ingredients into the dry ingredients, folding gently until just combined.
Fold in the walnuts before using an ice cream scoop to evenly distribute your batter into a lined muffin tin.
Bake at 350°F for 22-25 minutes or until a toothpick inserted into the middle comes out clean.
Let cool for 10 minutes before transferring to a rack.
Meanwhile, melt 1/4 cup butter and add the cinnamon + brown sugar to a plate.
Dip each muffin in butter and then swirl in the cinnamon sugar mixture. Enjoy warm!