Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners or grease it with cooking spray.

In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt until well combined.

In another bowl, beat the egg and then add in the milk, vegetable oil, vanilla extract, orange zest, and orange juice. Mix until fully incorporated.

Pour the wet ingredients into the dry ingredients and stir gently until just combined. Be careful not to overmix; a few lumps are okay.

Fold in the chocolate chips until evenly distributed throughout the batter.

Spoon the batter into the prepared muffin tin, filling each cup about ¾ full.

Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.

Allow the muffins to cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely.

If desired, dust with powdered sugar before serving for an extra touch of sweetness.