Preheat your oven to 350°F (175°C). Prepare a 9x5-inch loaf pan by greasing and flouring it, or lining with parchment paper.

In a large mixing bowl, cream together the softened butter and granulated sugar until the mixture is light and fluffy. Beat in the eggs one at a time, ensuring each is fully incorporated before adding the next.

Stir in the mashed bananas and vanilla extract until well combined. In a separate bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt.

Gradually add the dry ingredients to the wet ingredients, alternating with the milk, beginning and ending with the flour mixture. Mix until just combined; do not overmix.

Pour half of the batter into the prepared loaf pan. Dollop half of the chocolate hazelnut spread over the batter, then add the remaining batter on top.

Dollop the remaining chocolate hazelnut spread over the top layer of batter. Use a knife or skewer to gently swirl the chocolate through the batter, creating a marbled effect.

Bake for 50-60 minutes, or until a wooden skewer inserted into the center comes out clean. If the top browns too quickly, tent loosely with foil.

Allow the loaf to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.

While the cake cools, prepare the glaze: In a small bowl, whisk together the powdered sugar, unsweetened cocoa powder, and hot water until smooth. Adjust water for desired consistency.

Once the loaf is fully cooled, drizzle the cocoa glaze over the top. Slice and serve.