Preheat oven to 350. In bowl, combine oats, flour, brown sugar, walnuts, and baking soda. Beat in butter till course crumbs. Stir in chocolate chips. Reserve 3 cups of mixture, and pat the remaining in bottom of 15x10 jelly roll pan. Pour the brownie mix over the crust. Sprinkle the remaining mixture over the brownie mix and pat lightly.Bake 25 to 30 minutes. Cool completely. Cut into bars.