Pre-heat oven to 350F. Line a cookie sheet with parchment paper and set aside.
In a large bowl, mash the banana (should yield about 1/3 cup mashed). Add in the egg, butter, brown sugar, and vanilla. Whisk to combine.
Add the dry ingredients, flour, cinnamon, baking soda, salt, and chocolate chips, and mix just until combined (do not overmix or you will end up with cakey cookies).
The batter is naturally soft and not hard like normal chocolate chip cookies. Transfer batter to the freezer and allow to chill for about 30 minutes (optional step).
Scoop out the batter onto a baking sheet, about 2 inches apart. Bake for 10 minutes or until the cookies are lightly golden around the edges (the center should still be gooey). Cool for 5-10 minutes and enjoy!