Combine the flour, cocoa powder, salt, baking powder, baking soda, and cinnamon in a large mixing bowl.
Melt the unsweetened chocolate in the microwave at 50% power in 30 second increments.
In a separate mixing bowl, lightly beat the eggs. Add the melted chocolate, sugar, brown sugar, grated zucchini, oil, and vanilla extract and mix together.
Add the wet ingredients to the dry ingredients and stir until just moistened.
Spray 2 loaf pans with nonstick cooking spray. Pour in the batter, filling ⅔ full.
Bake at 325 degrees for 50-60 minutes until a toothpick inserted comes out clean.
Allow the bread to cool on a cooling rack, then remove from the pan and serve!