Preheat oven to 350 degrees and grease two 9×5 loaf pans.

Place the unsweetened chocolate in a large heatproof bowl with the vegetable oil and melt it on top of a pot of simmering water, creating a double boiler. Allow to cool slightly, then beat in the sugar, eggs, and yogurt.

In a small bowl, whisk together the flour, baking soda, baking powder, salt, and espresso powder. Add the dry ingredients to the chocolate mixture and gently stir to form a batter. Fold in the zucchini, then the chocolate chips. Divide the batter between the two pans and bake for 40-50 minutes, or until a toothpick inserted in the center comes out clean. Mine typically take 45 minutes. Cool for 15 minutes in the pans, then run a sharp knife around the edges and invert the loaves onto a cooling rack to finish cooling. This bread can be eaten warm and fresh, but I find it to be even more delicious after sitting overnight. It darkens, moistens, and becomes a dense, chocolately treat. I store it in the refrigerator and my kids love a cold slice after playing outside on a hot afternoon.