Ensure your oven rack is in the centre setting, and preheat to 350ºF. Grease the inside ends of the loaf pan, then line it with a strip of parchment paper, wide enough to cover the majority of the length of the pan, and up both long sides, with about an inch or two overhanging to act as handles.
Gently heat the butter in a small saucepan until melted. Remove from the heat and whisk in the espresso powder and vanilla until combined. Set aside to cool slightly.
Place the overripe bananas in the bowl of a stand mixer with the paddle attachment engaged. Turn the mixer to low and once the bananas are thoroughly mashed, add the melted butter-coffee-vanilla mixture, brown sugar, maple syrup, eggs, and yogurt. Mix on medium speed until well blended – about 1 minute.
Stop the mixer and add the flour, oats, baking soda, and salt. Mix on low just until about 90% blended, with some patches of dry flour still showing. Remove the bowl from the mixer and fold in the chocolate with a spatula – scraping the sides of the bowl to ensure the dry ingredients are incorporated. Do not over mix.
Pour the batter into the prepared pan and, if desired, top with a split banana, a sprinkle of oats, and some of the chocolate pieces. Bake for 55-65 minutes, or until a toothpick inserted in the centre of the loaf comes out clean or with just a few small crumbs. Let cool for 30 minutes, then lift the banana loaf out of the pan using the parchment paper handles. Set on a cooling rack to cool before slicing. Enjoy!