Preheat your oven to 350°F (175°C). Grease and flour a 9x13-inch baking pan.
In a medium bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt.
In a large bowl, beat the granulated sugar, brown sugar, and vegetable oil until well combined. Add eggs one at a time, beating well after each addition. Mix in vanilla extract.
Gradually add the dry ingredients to the wet mixture alternately with buttermilk, beginning and ending with dry ingredients. Stir until just combined.
Fold in the grated zucchini and chocolate chips.
Pour the batter into the prepared pan and smooth the top with a spatula.
Bake for 35-40 minutes, or until a toothpick inserted into the center comes out clean.
For the ganache, heat the heavy cream in a small saucepan until it just begins to simmer. Remove from heat and pour over the chopped chocolate. Let sit for 5 minutes, then stir until smooth.
Allow the cake to cool completely before spreading the ganache over the top.