Pre-heat oven to 350 degrees F.
In a large bowl whisk flour, walnuts, granulated and dark brown sugar, baking powder, salt, baking soda, nutmeg and allspice.
In a separate bowl, add mashed banana, melted butter, eggs and vanilla extract and mix until combined.
Add banana mix to flour and stir until well combined.
Pour batter in a lightly greased 9×5 loaf pan, until a toothpick inserted in the center comes out with a few moist crumbs, about 40-45 minutes, loosely covering the top with foil during the last 10 minutes.
Remove from oven and let cool for at least 30 minutes.
Serve & enjoy!