Preheat the oven to 160 degrees. Grease a 20x10 cm loaf pan with non-stick cooking spray or melted butter. Set aside.
In a large mixing bowl, mash 3 of the bananas. Whisk in the oil, maple syrup, eggs, vanilla and Greek yogurt.
Add in the flour, baking soda, spices and salt. Fold until just combined, being careful not to overmix (some lumps are okay!). Lastly, fold in the chocolate chunks.
Transfer batter to the prepared loaf pan. Split remaining banana in half, lengthwise, and place at the top of the batter.
Transfer to the oven and bake for 45-50 minutes, until a toothpick inserted into the center comes out clean. Let cool completely before removing from pan. Sprinkle with flaky sea salt, if desired.