Preheat the oven to 350°F (175°C). Grease a loaf pan or line it with parchment paper.
Mash the bananas and mix them with the melted butter.
Add the sugar, vanilla, and yogurt to the banana mixture and stir to combine.
In a separate bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
Add the dry ingredients to the wet ingredients and mix until just combined.
Fold in the walnuts, pour the batter into the loaf pan, and optionally sprinkle more nuts on top.
Bake for 55–65 minutes.(Tip: After about 40 minutes, loosely cover the top with aluminum foil to prevent over-browning.)
Let the banana bread cool in the pan for 15 minutes, then transfer to a wire rack to cool completely.