Preheat the oven to 190°C (375°F) and line a loaf tin with parchment paper. Set aside.
Start by mixing the milk and vinegar together in a large mixing bowl. Set aside while you grate the zucchini and prepare the other ingredients.
150 ml (⅔ cup) non-dairy milk, 1 teaspoon apple cider vinegar
Add the oil, sugar, vanilla to the milk mixture, and whisk to combine. Mix in the grated zucchini.
50 ml (¼ cup) olive oil, 80 grams (⅓ cup) sugar, 1 teaspoon vanilla, 200 grams (1 ½ cups) zucchini
Add the flour, cinnamon, baking powder, baking soda, and salt. Whisk to mix until just combined. Be careful not to overmix - a few streaks of flour are fine.
225 grams (1 ½ cups) whole grain spelt flour, 2 teaspoons cinnamon, 1 teaspoon baking powder, ½ teaspoon baking soda, ¼ teaspoon sea salt
Fold in the chocolate with a wooden spoon or spatula, and transfer the batter to the prepared loaf tin.
100 grams (½ cup) dark chocolate
Bake for 45-50 minutes, or until a skewer inserted in the centre of the loaf comes out clean (a couple small crumbs are fine).
Cool for about 15 minutes before carefully lifting out of the tin, then cool fully on a wire rack before slicing and serving. Leftovers can be stored for a day or two at room temperature, but should be refrigerated in warm weather.
Video
Notes
A standard loaf tin is 23x13cm (9x5 in.) if yours is a little longer and narrower (typical in Europe) that's fine, no need to change the baking time.