Begin by preheating your oven to 180C/350F (160C for fan ovens).
Prepare a large loaf tin (dimensions: 28 x 15 x 6.5cm / 11 x 6 x 2.5") by greasing it and lining it with baking paper.
Take the grated zucchini, squeeze out as much excess moisture as possible, and let it drain in a colander while you prepare the batter. (Note 4)
In a large mixing bowl, combine the flour, cocoa powder, baking soda, and salt. Whisk these dry ingredients together thoroughly.
In another bowl, whisk together the eggs and sugar until well blended. Add the melted butter and vanilla essence, continuing to whisk until the mixture is smooth and fully combined.
Pour the wet mixture into the bowl with the dry ingredients. Stir gently with a wooden spoon until the flour is just incorporated into the batter; it will be quite thick.
Fold in the grated zucchini and coarsely chopped chocolate. The batter will initially be very thick, but it will gradually become a thick, spreadable consistency.
Transfer the batter into the prepared loaf pan, smoothing the top. Bake for 45 minutes, then cover the bread with foil and continue baking for an additional 20 minutes. The bread is done when a skewer inserted into the center comes out clean, except for melted chocolate streaks.
Allow the bread to cool in the pan for 15 minutes before removing it. Then, transfer it to a cooling rack and let it cool for another 10 minutes before slicing.
This bread is exceptionally delightful when served warm, as the chocolate bits remain melty and the center stays extra fudgy!