Preheat oven to 350°F. Line baking sheets with parchment paper or reusable silicone baking mats. Set aside.
In the bowl of a stand mixer fitted with a paddle attachment (or using an electric hand mixer), cream together butter, brown sugar, granulated sugar, and vanilla extract until smooth. Scrape down bowl as needed.
Add mashed banana. Mix on low speed until combined. *Do not be alarmed. The batter may look separated or curdled after incorporating the banana.
In a separate bowl, whisk together flour, baking soda, kosher salt, and ground cinnamon. Add to mixing bowl. Mix on low speed until almost combined. Fold in chocolate chunks until well distributed and there are no longer any dry streaks of flour.
Portion out cookie dough using a size 24 scoop (2 ⅔ Tbsp). Place on prepared baking sheet, spacing them about 2-inches apart. Bake for 12-15 minutes, rotating baking sheet midway through baking. Immediately out of the oven, bang the hot baking sheet against a heat-proof hard surface. *This will deflate the puffed up cookie and help them flatten slightly like a traditional chocolate chip cookie.
Cool in pan for 3-5 minutes. Then, transfer cookies to wire rack. Enjoy cookies warm or cool to room temperature.