Preheat the oven to 350°F (175°C) and lightly spray or line a loaf pan.
In a medium bowl, mash the 3 overripe bananas with a potato masher until mostly smooth, then whisk in the olive oil, honey, beaten egg, and vanilla until combined.
In a large bowl, sift or whisk together the white whole-wheat flour, baking soda, salt, and ground cinnamon.
Add the wet banana mixture to the dry ingredients and stir gently with a wooden spoon or spatula until just combined; do not overmix.
Fold in the chopped walnuts and dark chocolate chips until evenly distributed.
Pour the batter into the prepared loaf pan and smooth the top.
Bake for 50–60 minutes, or until a toothpick or knife inserted in the center comes out clean.
Let the bread cool in the pan on a rack before removing and slicing.