Preheat oven to 350°F and line muffin pans with paper liners, sixteen liners in all.
Whisk together dry ingredients in a large bowl: flours, sugar, baking powder, baking soda, cinnamon, and salt. Set aside.
In a blender, place oil, milk, and spinach. Blend on high for about 30 seconds or until completely puréed. Add banana and vanilla; blend on low just to mix.
Pour puréed mixture into dry mixture and fold together until completely combined.
Fill muffin cups about ⅔ full and bake 18-20 minutes or until a toothpick inserted into the center comes out clean.
If serving to children: Call them Popeye's cupcakes For the holiday season, put a little red frosting or decor on it, or affix a holiday baking decoration. Put a strip of colour-appropriate frosting and a couple chocolate chips on it to make it a Ninja Turtle cupcake.