Preheat oven to 350 and grease a 9x5 inch bread pan.In a medium-large bowl combine zucchini, greek yogurt, sugars, eggs, and vanilla and mix well.Add flour, cocoa powder, baking soda, baking powder, and salt and mix until all ingredients are incorporated. Stir in 1 cup chocolate chips.Transfer batter to prepared bread pan and bake for 55-65 minutes until a toothpick inserted in the center of the bread comes out "dry" (it can have chocolate on it but shouldn't be covered in wet batter).Allow to cool completely, then gently run a knife around the edge of the pan to loosen the bread and remove it from the pan. Melt the remaining ¼ cup chocolate chips and drizzle or spread on top of bread.Slice and serve or store in an airtight container for 4-5 days (at room temperature) or 5-10 days (chilled). If you want to store the bread to serve later, I recommend letting the drizzled chocolate cool completely (10-20 mins) before transferring to an airtight container.