Preheat oven to 350 degrees F. Line two baking sheets with a Silpat baking mat or parchment paper. Set aside.
In a medium bowl, whisk together flour, baking soda, cinnamon, and salt. Set aside.
In a large mixing bowl, combine butter and sugars, mix until smooth. Add in egg and vanilla extract. Next, add the mashed banana and mix until combine.
Slowly add in the flour mixture and mix on low nuntil just combined. Stir in oats and chocolate chips.
Use a cookie scoop or two spoons to form the cookies into balls, using about 2 tablespoons of dough per cookie. Place cookies on prepared baking sheet, about 2 inches apart. Bake for 10 to 12 minutes or until golden around the edges but still soft in the center. Remove cookies from oven and let the cookies sit on the baking sheet for about 5 minutes. You can add chocolate chips to the warm cookies to make the cookies extra pretty, if desired. Just press them slightly into the cookies. Transfer the cookies to a cooling rack and cool completely.