Preheat the oven to 350F (180C or 170C on a convection oven). Line the bottom of a 9x5 inch (33x23 cm) loaf pan with baking paper and lightly grease the sides.
In a large bowl whisk together the flour, cinnamon, ginger, nutmeg, cloves, baking soda, baking powder and salt.
In a separate large bowl whisk together the melted butter, brown sugar, granulated sugar, eggs, vanilla, mashed bananas and pumpkin puree. There will be lumps from the banana, but you don't want to see pieces of egg or lumps of brown sugar.
Make a well in the middle of the dry ingredients and pour the wet ingredients into the well.
Gently fold the ingredients together using a rubber spatula or wooden spoon.
If adding in chopped walnuts, when the ingredients look about 70-80% combined, add in the chopped walnuts and fold in. Only mix the batter until combined. Some lumps from the banana are expected.
Spoon the batter into the prepared pan and smooth the top.
Bake in the preheated oven placing on a rack in the middle or bottom third of the oven. Bake for about 55-65 minutes, or until an inserted toothpick comes out clean or with a few crumbs. Check around 45 minutes. If the top is brown already but it is not done baking, tent a piece of aluminum foil over the pan.
Cool in the pan for at least 25 minutes before carefully transferring to a wire rack to continue cooling.