Preheat oven to 325°F (165°C). Lightly coat a 9 inch loaf pan with butter or olive oil. Set aside until needed.
In a large bowl, combine wet ingredients - eggs, olive oil, milk and vanilla extract. Beat lightly to combine, then add the sugar and mashed bananas, stirring together until combined.
In a smaller bowl, sift the dry ingredients together - flour, chocolate, baking powder, baking soda, salt, and spices. Then add the grated carrots and zucchini, stirring to coat.
Fold the dry ingredients into the wet ingredients. Fold only until ingredients are mixed together. Do not overbeat.
Pour the batter into the prepared loaf pan. Cut the remaining banana in half, lengthwise and place gently on the top of the batter, pressing down slightly. Sprinkle with raw sugar, if desired. Put pan in the oven.
Bake for 45 to 55 minutes. It's done when a skewer inserted in the center comes out with a few moist crumbs and no wet batter — or, more reliably, when the center registers 200 to 205°F on an instant-read thermometer.
Remove from oven and allow to cool in pan. Do not slice until completely cool or it will mash the bread.
Serve at room temp or cold. Store leftovers in the fridge.