Begin by preheating the oven to 350 degrees F.
In a large bowl, sift together the flour, baking soda, baking powder, and salt. Set aside.
In a stand mixer or large bowl with a hand mixer, combine the 3 Tbsp canola oil, unsalted butter, ripened bananas, and brown sugar.
Slowly and one at a time, add the eggs. Mix until evenly combined.
*The flour mix and the buttermilk will need to be added in increments to the banana mixture.*
Beginning and ending with the flour mix, slowly add the flour mix and the buttermilk alternately to the banana mix.
Spray the loaf pan with an even layer of baking spray.
In a microwave-proof bowl, microwave the Nutella with 1 tsp canola oil, about 20 seconds.
Add half of the banana batter to the loaf pan.
Drizzle half of the melted Nutella onto the batter and swirl into the batter using a knife.
Pour the other half of the batter into the loaf pan and top with the remaining Nutella.
Sprinkle with the chopped hazelnuts and bake in the oven for 50 minutes.
*One thing I always notice with banana nut breads is that they are often times dry, so we want to avoid that and keep the bread as moist as possible.*
Remove the bread from the oven and allow to cool on a wire rack.
Once the bread has cooled, melt the bittersweet chocolate in a double boiler and drizzle over the banana hazelnut bread. (Optional!)