Preheat oven to 350°F.
Combine spread and 1 tsp oil in a microwave-safe dish; microwave on high for 30 seconds or until melted. Stir.
Combine 3 Tbsp oil, butter, brown sugar, and banana in a large bowl; beat with a mixer at medium-high speed until well blended.
Add eggs 1 at a time, beating well after each addition.
Weigh or lightly spoon flour into dry measuring cups; level with a knife.
Combine flour, baking soda, baking powder, and salt.
Beating at low speed, add flour mixture and buttermilk alternately to banana mixture, beginning and ending with flour mixture; beat just until combined.
Coat pan with baking spray.
Scrape half of the batter into a 9x5 inch metal loaf pan and top with chocolate-hazelnut mixture.
Spread remaining batter over chocolate mixture.
Using a wooden pick, swirl batter.
Sprinkle batter with hazelnuts.
Bake at 350°F for 55 minutes or until a wooden pick comes out with moist crumbs clinging.
Cool 10 minutes in pan on a wire rack. Remove bread, cool on wire rack.
Place bittersweet chocolate in a microwave-safe dish; microwave on high for 30 seconds. Drizzle bread with chocolate; let stand until set.