Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper. Set aside.
In a medium mixing bowl, mash the banana with a fork until smooth. Set aside.
In a large bowl, whisk together the melted butter and brown sugar until smooth and creamy. Add the mashed banana, egg, and vanilla extract. Mix until fully incorporated.
In a separate bowl, whisk together the flour, ground cinnamon, baking soda, and salt.
Gradually add the dry ingredients into the wet mixture. Stir until just combined, being careful not to overmix.
Gently fold in the chocolate chips and chopped chocolate bar until evenly distributed.
Using a medium cookie scoop or tablespoon, drop the dough onto the prepared baking sheets, spacing them about 2 inches apart.
Bake the cookies for 10-12 minutes, or until the edges are set and the centers look slightly underbaked.
Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.
