Prep: Preheat oven to 350°F (175°C). Grease a 9x5-inch loaf pan.
Mash Bananas: In a bowl, mash bananas until smooth (small lumps okay).
Mix Wet Ingredients: Whisk in melted butter, egg, sugar, and vanilla.
Combine Dry Ingredients: In another bowl, mix flour, baking soda, salt, and cinnamon.
Combine: Gently fold dry ingredients into wet until just combined (do not overmix).
Add-Ins: Fold in nuts/chocolate if using.
Bake: Pour batter into the pan. Bake 50–60 minutes, or until a toothpick comes out clean.
Cool: Let rest in pan for 10 minutes, then transfer to a rack to cool completely.