Preheat oven to 350 F.
Mash bananas until puree like consistency. Set aside.
In a large bowl combine butter and sugars. Beat on low with an electric hand mixer or stand mixer until smooth and creamy. Add egg, vanilla, bananas. Mix on low until combined. Set aside.
In a separate medium bowl, combine sifted flour and baking soda, baking powder, salt, and oats. Whisk to combine and add to wet ingredients gradually. Add ½ or 1 cup at a time, beat on low until combined, and then continue with the next batch.
Mix until ingredients are almost combined.
Fold in chocolate chips.
Scoop 2 tablespoonfuls of dough and roll into balls. I like these cookies to be thick and rich but you can make smaller ones by using just 1 ½ tablespoons of dough per one cookie ball.
Arrange the cookie balls on a baking sheet lined with parchment paper or silicone mat cookie sheet. These cookies need to be at least 2 inches apart. Don’t press them down!
Bake for 11-13 minutes (the time varies due to different ovens) until golden brown top. By the end of baking, the cookies should be soft in the middle and have risen up slightly.
The cookies will have a quite soft center inside. Once they cool down they will set well and the texture inside remains soft, lots of banana flavor and with a creamy buttery flavor. For the chocolate chips, I like to decorate the cookies after they have baked by pressing 4-5 chocolate chips on top of the cookies.
Let cool in the baking sheet for 5-10 minutes and then transfer to a wire rack.