Preheat oven to 350°F. Grease and flour a 9-inch round baking pan. Set aside.
In a large bowl, whisk together sugar, flour, cocoa powder, instant coffee granules, baking powder, baking soda and salt.
Add in the egg, milk, olive oil, vanilla extract, boiling water and shredded zucchini. Stir until just combined.
Pour batter into your prepared pan, using a rubber spatula to scrape it out of the mixing bowl. Tap your pan on the counter to release any excess air bubbles.
Place cake in oven to bake for 30–35 minutes, or until a toothpick inserted into the center comes out clean. Remove from oven and place on a wire rack to cool completely before frosting. To make chocolate frosting, blend softened butter in a large bowl until smooth. Mix in powdered sugar 1 cup at a time. Add vanilla extract, milk, cocoa powder and melted chocolate.
Continue blending until just combined.
Evenly spread this frosting on top of your cooled cake. Slice, serve and enjoy.