Preheat oven to 180C / 350F. Line a 12-cup muffin tin with cupcake liners. Line a second muffin tin with 4 cupcake liners.
Place bananas, zucchini, carrot, eggs, maple syrup, vanilla extract and coconut oil in a blender or food processor. Process to a smooth puree.
Add the puree to a large bowl. Add flour, cocoa powder, baking powder, baking soda and salt. Gently stir until just combined.
Add chocolate chips. Fold in gently.
Pour ¼ cup batter into each cupcake liner. Do not overfill.
Transfer muffin tins to oven. Bake for about 20-25 minutes or until a skewer inserted into the center of the muffins comes out clean.
Cool in pan for 10 minutes before transferring the muffins into a wire rack to cool completely.