Preheat the oven to 350 degrees and grease an 8-1/2 x 4-1/2 loaf pan with nonstick cooking spray.
Place the butter in a large microwave-safe mixing bowl and microwave for one minute, or until just melted. Stir in the brown sugar until completely smooth. Add the eggs and vanilla and stir until incorporated. (Be sure to add the eggs after the brown sugar is mixed in, as the hot butter alone could cook the eggs.)
Whisk together the flour, cocoa powder, salt, baking powder, baking soda and instant coffee (if using) in a medium bowl. Add to the butter mixture and stir until well combined. It will be very thick.
Stir in the shredded zucchini and chocolate chips. (It will still be thick -- that's okay.)
Spoon the batter into the prepared loaf pan and spread evenly. Bake for 60-65 minutes, or until a toothpick or cake tester inserted into the center comes out clean (save for perhaps a smear from the melted chocolate chips). Let the loaf cool on a rack for about 10 minutes before turning out onto a rack to cool completely.