Heat oven to 350°F/175°C. Line a loaf pan with parchment paper.
Mash bananas in a large bowl. Whisk in eggs, sugar, olive oil, and vanilla until smooth.
Add flour, baking powder, baking soda, and remaining baking powder. Stir until just combined. Fold in dark chocolate, white chocolate, and walnuts.
Pour batter into the prepared pan. Arrange banana halves on top.
Bake until golden and a tester comes out clean, 40 to 45 minutes. Cool completely before slicing.