Preheat oven to 350°. Lightly grease 8 x 4 inch loaf pan.
In small bowl, combine ground flax meal and 6 tbsp water to make flax egg. Set aside and let sit for 5-10 minutes.
In a large bowl or stand mixer, cream together vegan butter and cane sugar for 2-3 minutes.
Coarsely grate zucchini and combine with creamed butter and sugar. Add water and vanilla extract.
In a separate bowl, whisk together flour, baking soda, baking powder, and salt.
Add dry ingredients into bowl with wet ingredients. Mix to combine.
Divide the batter in half. Add cocoa powder into one bowl of batter and cardamom into the other. Stir each until well-mixed.
Pour the chocolate batter into one half of loaf pan and pour cardamom batter into the other. Using a butter knife, swirl cocoa and cardamom batter together. Sprinkle top with cane sugar (optional).
Bake for 60-70 minutes or until toothpick comes out clean. Let cool for 15 minutes, then gently turn upside down to remove from pan. Let cool on wire rack.