Preheat the oven to 350 degree Fahrenheit. Butter a 9 by 5 inch loaf pan. Mix together the flour, sugar, cocoa powder, baking powder, and nutmeg, ground ginger, salt in a large bowl. In another bowl, cream, the butter until lightened, then beat in the chocolate, eggs, banana, and vanilla. Stir in the dry ingredients just until combined. Do not over-beat.
Pour the batter into the load pan and bake until a toothpick stuck into the center of the bread comes out almost clean. 50 to 60 minutes minutes. Transfer the pan to a rack and cool for at lead 15 minutes before un-molding.