Preheat oven to 350F. Line a 9×5 loaf pan with parchment paper and set aside.
In a large bowl, whisk mashed bananas, both sugars, oil, 1/4 cup peanut butter, eggs, and vanilla until smooth. In a separate medium bowl, whisk flour, baking soda, and salt.
Add flour mixture to liquid mixture, gently folding until batter is just combined. Spread batter evenly in prepared pan, drop remaining 1/4 cup peanut butter by the small spoonfuls on top, and use a knife to swirl into batter.
Bake banana bread at 350F 55-60 minutes until a toothpick inserted in center comes out clean.
Cool banana bread completely on a wire cooling rack. Remove bread from pan and cut into slices for serving. Enjoy!