Spray 2 baking sheets with nonstick cooking spray and preheat oven to 350 degrees F.
In a large bowl, beat the first 5 ingredients with an electric mixer until well mixed.
In a separate bowl, mix the flour and baking soda until well combined, add to the banana mixture and mix well. Gently fold in the walnuts.
Drop the dough by rounded teaspoonfuls 2-3 inches apart on the baking sheets. Bake sheets 1 at a time until light brown, about 12-15 minutes. Remove cookies from baking sheet and place on a cooling rack.