Preheat oven to 350℉/177℃.
In a small bowl, mix mashed bananas, pumpkin puree, sour cream, and eggs.
Add the brown sugar, granulated sugar, and vanilla into the wet batter, and mix until smooth; set aside.
Gradually add the dry ingredients into the wet ingredients - Flour, baking powder, baking soda, cinnamon, nutmeg, ginger, allspice, orange zest, and salt; mix until fully combined.
Pour in melted butter, and continue to stir until the butter has been fully incorporated into the mixture.
Grease an 8x4 or 9×5 loaf pan with cooking spray or butter.
Scrape down the sides and pour the batter into the greased pan and spread evenly. Or divide the batter between two greased bread pans.
Add the desired toppings or leave the bread plain. Mix in chocolate chips if making chocolate pumpkin bread. Or top with chopped nuts.
Bake for 55-60 minutes (if you divided the batter between two bread pans, start checking it at 30 minutes) or until a cake tester inserted into the center comes out clean.
Let the pumpkin banana bread remain in the pan(s) for about 10 minutes before removing, then turn out onto a wire rack to cool completely.
Drizzle with sauce if desired.