Heat the oven to 350° and coat 16 muffin cups with cooking spray. In a large bowl, whisk together all-purpose and whole wheat flours, sugar, baking powder, baking soda and salt, and cinnamon. In a blender, puree canola oil, milk, and baby spinach until smooth, then blend in banana and vanilla. Fold the liquid mixture into the dry ingredients. Fill each prepared muffin well two-thirds full. Bake the muffins until a toothpick inserted in the center comes out clean, about 18 minutes.