Preheat oven to 400 degrees F.
In a large bowl combine dry ingredients: flour, oat bran, baking powder, baking soda, cocoa powder, sugar, and chocolate chips.
Stir to combine dry ingredients.
Add in skim milk, egg, and vanilla, stir just until wet.
Slowly pour in coconut oil, stir just until combined.
Pour muffin batter into a muffin pan lined with cupcake wrappers.
Fill each muffin cup ¾ full.
Bake in the oven 15-20 minutes or until a cake tester comes out clean from the center of the muffins.