Preheat oven to 350°F / 200°C and line a baking sheet with parchment paper.
In a large bowl, mix dry ingredients, flour, oats, baking soda, baking powder, and salt, set aside.
In your mixing bowl or medium large bowl, combine the egg, mashed banana, sugars, butter, and vanilla extract and mix very well until smooth.
Gradually add dry ingredients to the wet ingredients, and mix on low until incorporated. Don't over-mix.
Incorporate the chocolate chips into the batter, ensuring thorough and even distribution.
Scoop about a tablespoon (or use an ice cream scoop) of batter onto the prepared baking sheet.
Bake for about 10 to 14 minutes, or until edges are golden brown.
Let cookies cool for at least 10 minutes and enjoy warm or cool.