Preheat the oven to 350°F and line a baking sheet with parchment paper.
Mash the ripe bananas in a bowl until smooth, then stir in the melted butter, sugar, egg, and vanilla.
In another bowl, whisk together flour, baking soda, salt, and cinnamon.
Combine the wet and dry ingredients, then fold in oats and chocolate chips if using.
Scoop spoonfuls of dough onto the baking sheet, leaving space between them.
Bake for 10–12 minutes until golden on the edges and set in the middle.
Let cool on a wire rack before serving.