In a large bowl, combine all the dry ingredients: flour, cocoa powder, granulated sugar, brown sugar, and baking powder. Mix well.
In another bowl, combine the milk, egg, melted butter, and vanilla extract. Mix until smooth.
Gradually pour the liquid mixture into the dry ingredients, mixing gently until fully incorporated.
Wash, peel, and finely grate the zucchini. Add the grated zucchini to the batter and fold gently.
Preheat the air fryer to 180°C.
Fold 120 g of chocolate chips into the batter, mixing gently.
Line muffin tins with paper liners and lightly spray with oil. Fill each cup about ¾ full.
Distribute the remaining chocolate chips on top of each muffin.
Place the muffin tins in the air fryer basket and cook at 180°C for 12 minutes.
Check doneness by inserting a toothpick in the center: if it comes out clean, the muffins are ready. If not, continue cooking, checking every minute.
Remove the muffins from the air fryer and let cool before removing from the liners.