Preheat oven to 175°C (350°F) and prepare a loaf pan with grease or parchment paper to ensure easy removal.
Whisk together flour, baking soda, baking powder, spices, and salt in a bowl to evenly distribute dry ingredients.
In another bowl, mix mashed bananas, pumpkin purée, eggs, oil, sugars, and vanilla until smooth and well combined.
Gently fold dry ingredients into wet mixture until just combined, being careful not to overmix the batter.
Fold in optional nuts or chocolate chips for added texture and flavor variation.
Pour batter into pan and bake for 55–60 minutes until a toothpick inserted comes out clean.
Cool in pan briefly, then transfer to a rack and allow to cool completely before slicing for best texture.