Preheat the oven.

Mix melted butter and sugar in a bowl.

Add eggs and vanilla; mix until combined.

In a separate bowl, combine flour and baking soda.

Gradually add the dry ingredients to the wet mixture, then fold in the mashed bananas.

Prepare the cinnamon sugar swirl by mixing melted butter, granulated sugar, dark brown sugar, and ground cinnamon in a small bowl.

Pour half of the banana batter into a greased loaf pan.

Add half of the cinnamon sugar mixture over the batter.

Pour the remaining banana batter on top and finish with the remaining cinnamon sugar mixture.

Use a knife to swirl the mixture gently.

Arrange banana slices on top for garnishing.

Bake until golden brown and a toothpick comes out clean.

Allow to cool before slicing.