1. Preheat your oven to 350°F (175°C) and grease a 9×5-inch loaf pan.
2. In a large bowl, mix mashed bananas, melted butter, sugar, eggs, and vanilla until smooth.
3. In another bowl, whisk together flour, baking soda, and salt. Gradually fold the dry ingredients into the wet mixture until just combined.
4. In a small bowl, mix peanut butter and melted chocolate.
5. Pour half of the banana batter into the loaf pan. Add dollops of the peanut butter-chocolate mixture and swirl with a knife. Repeat with the remaining batter and swirl on top.
6. Bake for 50-60 minutes or until a toothpick inserted in the center comes out clean. Cool for 10 minutes before removing from the pan.
7. Optionally, drizzle extra melted peanut butter on top before serving.