Preheat oven to 350°F (175°C). Grease a 9×5-inch loaf pan or line with parchment paper.
In a large bowl, mash bananas. Stir in melted butter, sugar, eggs, and vanilla until well combined.
In a separate bowl, whisk together flour, baking soda, salt (and cinnamon if using).
Gradually mix the dry ingredients into the wet mixture just until combined.
Fold in chocolate chips (and walnuts if using).
Pour batter into the prepared loaf pan. Smooth the top and sprinkle a few chocolate chips over it.
Bake for 50–60 minutes or until a toothpick inserted in the center comes out clean or with moist crumbs.
Cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.