Preheat your oven to 350°F (175°C) and grease a 9×5-inch loaf pan with butter or non-stick spray. Line with parchment paper for easy removal later.
In a large mixing bowl, mash the bananas until almost smooth but with some small chunks remaining for texture. Stir in the melted butter until well combined.
Add sugar, egg, and vanilla to the banana mixture, mixing thoroughly after each addition.
Sprinkle the baking soda and salt over the wet mixture. Fold in the flour gently using a spatula, mixing just until no dry streaks remain.
Fold in 1/2 cup of the chopped walnuts, saving the remaining 1/4 cup for topping.
In a separate bowl, beat the softened cream cheese until smooth and fluffy. Add sugar and continue beating until well incorporated. Mix in the egg and vanilla extract until the mixture is silky and uniform.
Pour two-thirds of the banana bread batter into the prepared loaf pan. Spoon the cream cheese mixture on top in an even layer. Add the remaining banana bread batter in dollops across the surface.
Use a butter knife or skewer to create gentle swirls by dragging through the batters. Avoid over-swirling, which can muddy the distinct layers.
Sprinkle the remaining walnuts across the top of the loaf.
Bake in the preheated oven for 55-65 minutes, or until a toothpick inserted into the center comes out clean with a few moist crumbs. If the top browns too quickly, cover loosely with aluminum foil during the last 15-20 minutes of baking.
Allow the bread to cool in the pan for 10 minutes before transferring to a wire rack to cool completely for at least 20 minutes before slicing.