Begin by preheating your oven to 350°F. Lightly grease an 8½ x 4½-inch loaf pan and set it aside.
In a medium mixing bowl, sift or whisk together the flour, baking soda, salt, cinnamon, and nutmeg. This ensures the spices and leavening agents are well distributed.
In a separate large mixing bowl, combine the mashed bananas, melted butter, sugar, egg, and vanilla extract. Whisk until the mixture is smooth and well-blended.
Gradually incorporate the dry ingredients into the wet mixture, stirring gently until just combined. Be careful not to overmix to keep the bread tender. Fold in the chopped walnuts evenly throughout the batter.
Pour the prepared batter into the greased loaf pan. Place the pan in the preheated oven and bake for 50-60 minutes, or until the bread is golden brown and a toothpick inserted into the center comes out clean. Avoid overbaking to keep the bread moist.
Once baked, remove the loaf from the oven, carefully take it out of the pan, and allow it to cool completely on a wire rack before slicing and serving.