Preheat your oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan.
In a large bowl, mash the ripe bananas until smooth. Stir in melted butter, sugar, eggs, and vanilla until well combined.
In another bowl, whisk together flour, baking soda, salt, and cinnamon (if using).
Gradually fold the dry ingredients into the wet mixture until just combined—do not overmix.
Gently fold in the chopped nuts.
Pour the batter into the prepared loaf pan and smooth the top.
Bake for 50–60 minutes, or until a toothpick inserted in the center comes out clean.
Cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.