Preheat the oven to 350°F (175°C). Grease or line a 9x5-inch loaf pan with parchment paper.
Mash the bananas in a large mixing bowl until smooth with a few chunks remaining.
Mix the wet ingredients: Add the peanut butter, melted butter (or oil), brown sugar, eggs, and vanilla extract to the mashed bananas. Stir well until fully combined.
Whisk together dry ingredients: In a separate bowl, combine the flour, baking soda, and salt.
Combine the wet and dry ingredients: Gradually fold the dry ingredients into the wet mixture, stirring until just combined. Avoid overmixing.
Add optional ingredients: If desired, fold in chocolate chips or chopped peanuts for extra flavor and texture.
Pour the batter into the prepared loaf pan and spread it evenly.
Bake for 55-65 minutes, or until a toothpick inserted into the center comes out clean. If the top starts to brown too quickly, cover with aluminum foil for the last 10-15 minutes.
Cool the bread in the pan for about 10 minutes before transferring it to a wire rack to cool completely.
Serve: Slice and enjoy!