Preheat oven to 350°F. Grease the bottom and 1/2 inch up the sides of two 8x4x2-inch loaf pans; set aside. In a large bowl stir together flour, baking powder, cinnamon, and salt. Make a well in the center of flour mixture.
In a medium bowl combine eggs, zucchini, sugar, oil, and vanilla. Add zucchini mixture all at once to flour mixture. Stir just until moistened (batter should be lumpy). Fold in nuts (if desired) and 3/4 cup of the chocolate pieces. Pour batter into the prepared loaf pans, spreading evenly.
Bake about 55 minutes or until a toothpick inserted near the centers comes out clean. Cool in pans on a wire rack for 10 minutes. Remove from pans; cool completely on rack.
In a small saucepan cook and stir the remaining 1/2 cup chocolate pieces over low heat until melted. Drizzle melted chocolate over loaves. Wrap and store overnight before slicing.