Preheat oven to 350 degrees and line your cookie sheets with parchment paper.
In a large bowl or your stand mixer, combine butter, brown sugar, sugar, egg, vanilla extract and mashed bananas. I like to combine the egg, butter and bananas first.
Next add flour, cinnamon, baking soda, cloves and cornstarch and mix.
Finally add in oats.
Using a tablespoon cookie scoop, place dough onto a cookie sheet. Flatten dough with the back of the scoop a little bit so it forms a disk shape. The dough will be a little sticky. Your oatmeal banana cookies will spread a little when baked.
Bake for 10-12 minutes or until edges just start to turn brown.
Cool on cookie sheet for 3-4 minutes, then move to cooling rack with a cookie spatula to finish cooling.