Assemble ingredients and tools.
Preheat oven to 425 degrees. Grease a 12-cup muffin tin.
In a medium bowl or two cup measure, whisk together the melted butter or oil, Maine maple syrup, egg and plain yogurt.
In a large bowl, combine the whole-wheat pastry flour, baking powder, baking soda, and cinnamon.
Grate the zucchini.
Pour the wet ingredients into the bowl with the flour. Add the grated zucchini and chocolate chips. Using a spatula or large spoon, fold the ingredients gently to mix, being careful not to work the batter too much.
Portion the batter into the greased muffin tin.
Bake at 425 degrees for 5 minutes, then reduce the oven heat to 350 degrees and bake until a toothpick comes out clean, about 12 – 15 minutes. Remove the pan from the oven and let rest for 5 minutes.
Turn muffins out onto a rack and cool completely. Store tightly wrapped or in a tin. These muffins also freeze well. Makes 12 muffins.