Preheat your oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners or grease the muffin cups.
In a large mixing bowl, mash the ripe bananas with a fork until smooth. Stir in the melted butter.
Add the granulated sugar, brown sugar, beaten egg, and vanilla extract. Mix until combined.
Sprinkle the baking soda and salt over the banana mixture and stir. Gently fold in the flour and cinnamon (if using) until just combined. Be careful not to overmix.
If using, fold in the chopped walnuts or chocolate chips.
Evenly divide the batter between the prepared muffin cups, filling each about ⅔ full.
Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Let the muffins cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.