Preheat your oven to 350°F (175°C) and grease a 9x5 inch loaf pan.
In a large bowl, mash the ripe bananas until smooth.
Add the peanut butter, sugar, eggs, and vanilla to the bananas, mixing well.
In another bowl, combine the flour, baking soda, and salt.
Gradually add the dry ingredients to the wet mixture, stirring until just combined.
If using, fold in the chopped walnuts for added crunch.
Pour the batter into the prepared loaf pan.
Bake in the preheated oven for 55-60 minutes, or until a toothpick comes out clean.
Allow the bread to cool in the pan for 10 minutes, then transfer to a wire rack.
Slice and enjoy your delicious peanut butter banana bread!