Preheat oven to 375 degrees. Line 2 baking sheets with parchment or spray with nonstick spray.
In the bowl of your mixer cream together the butter and sugars until light and fluffy.
Beat in the eggs and vanilla.
In a separate bowl stir together the flour, oatmeal, baking soda, cinnamon, and salt.
Add the dry ingredients to the butter and sugar and beat until just combined.
Mix in the mashed bananas and walnuts until well incorporated.
Use a large cookie scoop to drop scoops of cookie dough onto the prepared baking sheets. Bake on the middle rack for 12 minutes or until the edges are browned and cookies are set.
Cool on a wire rack.
Notes
The chopped walnuts are optional but we enjoy the crunchy texture and nutty flavor that they add to the cookies!