Preheat oven to 350oF (180oC).Line a standard 12 cups muffin pan with cupcake liners. Set aside. To a bowl, add sugar and orange juice. Whisk until sugar is completely dissolved.
Then add oil and mix well.
Sift in flour, cocoa powder, baking powder, baking soda and salt.
Mix until dry flour is no longer visible. DO NOT OVER MIX (mix until dry and wet ingredients are just combined).
Spoon batter into cupcake liner until 2/3 full.
Add orange zest on top of cupcakes (optional).
Bake in preheated oven to 350oF (180oC), rack middle position, 18-20 minutes, or until toothpick inserted in the middle of cake comes out clean.
Let cupcakes cool down in pan for 10 minutes. Then transfer cupcakes to wire rack to cool down completely.