Preheat oven at 350 degrees. Grease bottom and sides of rectangular pan, 13x9x2 and set aside.
In a medium bowl combine the flour, baking soda & salt. Set aside.
In a large bowl, cream the butter and sugar until light and fluffy. Add the eggs, bananas & vanilla extract.
Gradually add the flour mix into the creamed mixture and continue beating on medium speed for about 2 minutes. Fold in the chocolate chips with a spatula. Do not over mix.
Pour mixture into prepared baking pan and bake for 25 minutes or until a toothpick inserted near the center comes out clean (do not overbake).
Cool in pan for about 20 minutes.
For the frosting cream butter and cream cheese in a mixing bowl. Gradually add confectioners’ sugar and vanilla. Beat well. If you want it thicker add a littler more confectioners’ sugar. Spread over bars.
For frosting, in a large bowl, beat the cream cheese until fluffy. Gradually beat in enough confectioners' sugar to achieve desired consistency.
Frost bars and top with the chopped walnuts. Store in the refrigerator.