For the banana bread:
1 cup / 4.5 oz / 125g all-purpose flour
1 cup / 5 oz / 140g whole wheat flour
3/4 cup / 4.5 oz / 125 g dark muscovado or dark brown sugar
3/4 teaspoon baking soda
1/2 teaspoon kosher salt
1 cup / 4 oz / 115 g coarsely chopped bittersweet chocolate
1/3 cup / 80 ml extra-virgin olive oil
2 large eggs, lightly beaten
1 1/2 cups / 12 oz / 340 g mashed, VERY ripe bananas (~3 bananas)
1/4 cup / 60 ml plain, whole milk yogurt
1 teaspoon freshly grated lemon zest
1 teaspoon vanilla extract
For the glaze:
1/2 cup / 3 oz / 85 g sifted dark muscovado or dark brown sugar
1/2 cup / 2 oz / 55g confectioners' sugar
4 teaspoons freshly squeezed lemon juice
Preheat the oven to 350° F, and place a rack in the center. Grease a 9- by 5- inch (23 x 13 cm) loaf pan, or equivalent.
In a large bowl, whisk together the flours, sugar, baking soda, and salt. Add the chocolate pieces and combine well.
In a separate bowl, mix together the olive oil, eggs, mashed banana, yogurt, zest, and vanilla. Pour the banana mixture into the flour mixture and fold with a spatula until just combined. Scrape the batter into the prepared pan and bake until golden brown, about 50 minutes. You want to get that beautiful color on the cake, but at the same time you don't want to bake all the moisture out of it. So the minute you're in that zone, pull it. Erring on the side of under-baking versus over.
Transfer the pan to a wire rack to cool in the pan for 10 minutes, then turn the loaf out of the pan to cool completely.
While the cake is cooling, prepare the glaze. In a bowl, whisk together the sugars and the lemon juice until smooth. When the cake is completely cool, drizzle the glaze on top of the cake, spreading with a spatula to cover.