For the orange-chocolate muffins, preheat the oven to 200 degrees and line a muffin tin for 12 with paper cups.
Mix flour with baking powder, chocolate chips, orange zest and salt in a bowl.
In a large bowl, whisk egg with oil, sugar, orange juice and buttermilk. Fold the flour mixture into the egg mixture.
Pour the batter into the muffin cups and bake the orange-chocolate muffins for about 20 to 25 minutes in the oven at 200 degrees.