Preheat your oven to 350°F (180°C) and prepare a 20 cm loaf pan by lining it or greasing it.

Combine milk and apple cider vinegar in a bowl and let it sit for 5 minutes.

Grate zucchini, wrap in a paper towel, and squeeze out excess moisture.

In a bowl, beat egg, mashed banana, maple syrup, vegetable oil (or melted butter), and vanilla until creamy.

Fold the squeezed zucchini into the wet mixture.

Sift together oat flour, cocoa powder, baking powder, and baking soda; add it to the wet mixture until no lumps remain.

Mix in the milk and vinegar mixture until evenly combined.

Fold in chocolate chips, reserving some for the top.

Pour the batter into the loaf pan and bake for 30-40 minutes until a toothpick comes out clean.

Let the bread cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.