Add 1 tsp salt to the grated zucchini and leave it in a strainer over a bowl for around 15 minutes. Also use this time to make the flax egg by combining the flaxseed and water.
After 15 minutes, press down lightly on the zucchini and pat it dry with a paper towel. Transfer to a large mixing bowl with 1/2 cup zucchini water and the plant based milk. Next, add the flax egg, mix, and follow it up with the chopped cilantro and onion.
Add the flour slowly and combine with the rest of the ingredients, but make sure not to over-mix. Right at the end, add the rest of the salt.
Line a loaf tin with a sheet of parchment paper, making sure to leave a little bit hanging over the edges. Pour the batter into the loaf tin and spread it out with a spatula. Bake in the preheated oven for 40-45 minutes, until a toothpick comes out clean from the centre.
Transfer to a cooling rack and leave to cool for around 5-10 minutes before serving.