Preheat the oven to 350˚F.
In a small bowl, combine the Nutella and 1 teaspoon canola oil and microwave for 30 minutes, or until melted. Set aside.
In a separate bowl, combine the milk and vinegar, and set aside to “sour”.
In a large bowl mix together the remaining 3 tablespoons of canola oil, butter, brown sugar and banana using a mixer on medium speed. Beat until well blended. Add the eggs one at a time, beating well after each addition.
In a separate bowl, mix together the flour, baking soda, baking powder and salt.
Beating at low speed, add the flour mixture and “soured” milk alternately to banana mixture until fully incorporated.
Pour half of the mixture into a lightly sprayed loaf pan. Top with chocolate mixture. Pour the remaining batter over the chocolate mixture. Using a wooden pick, swirl the batter. Sprinkle with hazelnuts.
Bake for 55 minutes, or until a toothpick inserted comes out with moist crumbs clinging. Let cool in the pan for 10 minutes, then remove to cool on wire racks.