Preheat the oven to 400ºF. Spray a 12 cup muffin pan with cooking spray or line with paper liners.
In a large bowl, combine all-purpose flour, whole wheat flour, sugar, baking powder and salt.
In a small bowl combine milk, vegetable oil, vanilla extract, and eggs.
Make a well in the center of the dry ingredients. Add the wet ingredients and stir together quickly with a rubber scraper. Its ok if there are still a few dry spots.
Gently fold in the zucchini and chocolate chips, if desired, until everything is combined.
Divide evenly amongst the muffin cups. Bake 20 minutes or until golden brown and a toothpick inserted in the center of a muffin comes out clean. Cool briefly in the pan before removing to a cooling rack to cool completely.