Preheat the oven to 200°C and line the muffin pan with 12 muffin liners. Set aside.
To make a flax egg, combine a flax meal with water. Mix well and set aside for about 10 minutes to thicken.
To the medium-size bowl, add all-purpose flour, cocoa powder, baking powder, baking soda, and a pinch of sea salt. Mix with a whisk to combine.
To a large bowl, add cane sugar, sunflower oil, vegan yogurt, and flax egg. Mix with a whisk until well combined. Add oat milk and apple cider vinegar and whisk to combine.
To the wet mixture, sift dry ingredients, and mix together until just combined. Be careful not to overmix. Squeeze excess water out of the grated zucchini, then stir it into the batter.
Evenly divide the batter into 12 muffin liners and top with chocolate chips.
Bake in preheated oven at 200°C for 5 min, then turn the oven to 180°C and bake for 25-30 min. The muffins are done when a toothpick inserted into the middle comes out clean. If it looks wet, bake for another 5 minutes because ovens can vary.
Let the muffins cool in the pan for about 10-15 minutes, then add to the cooling rack and let cool completely.