Preheat your oven to 350°F (175°C). Grease and flour a standard loaf pan or two mini loaf pans , or line it with parchment paper for easy removal.
In a large mixing bowl, whisk together the all-purpose flour, almond flour, cornstarch, sugar, salt, and baking powder. Make sure the dry ingredients are well combined.
In a separate bowl, combine the mashed banana, light olive oil, and almond milk.
Gradually add the wet ingredients to the dry ingredients, mixing until just combined.
Pour half of the batter into the prepared loaf pan and spread it evenly.
Evenly spread 3 Tbsp of nutella over the batter.
Pour the remaining banana bread batter over the nutella, spreading it carefully to cover.
Spread another 1 Tbsp of Nutella over the top of the batter and use a swirling motion with the back of a spoon to create a marbled top effect.
Bake the banana bread in the pre-heated oven for about 50-60 minutes (for a standard loaf) or 30 minutes for 2 mini loaves.
Once baked, remove the loaf from the oven and allow it to cool in the pan for about 10 minutes. Then, transfer it to a wire rack to cool completely.
Slice and enjoy