Preheat the oven to 350°F (170°C or 160°C for a fan oven).
Grease or line two large loaf pans.
Combine the flour, cocoa, sugar, baking powder, baking soda, cinnamon, nutmeg and salt in a very large bowl. Stir to mix thoroughly.
Stir in the chopped cranberries and walnuts. Set aside.
In a medium bowl, beat the eggs.
Add the olive oil and vanilla and beat together well.
Stir in the shredded zucchini (courgette).
Gradually add the wet ingredients to the dry ingredients, stirring gently as you go. Be sure to blend in all the dry ingredients, but only until just mixed. Do not beat.
The batter will be very thick at this point, but don't be tempted to add any more liquid. The thick batter gives the most luscious cake!
Scoop the batter into the loaf pans, levelling the top a little.
Bake for 40 to 50 minutes, or until a skewer inserted in the centre of the loaves comes out clean.
Cool in the loaf pans for 15 minutes.
Remove the loaves from the loaf pans carefully and cool completely on wire racks.
When the loaves are completely cool, make the glaze.
Combine the icing sugar (confectioner's sugar) and cinnamon.
Gradually add the water, a bit at a time, beating until a smooth, drizzle-able consistency is reached. You may not need all the water.
Drizzle the glaze over the loaves and allow the glaze to set before cutting.