In a large bowl, combine oats, flour, brown sugar, baking soda and salt.
Cut in butter until mixture resembles coarse crumbs.
Press into a greased 13-in. x 9-in. x 2-in. baking pan.
In a saucepan, combine dates, sugar and water. Cook for 10 minutes or until thickened, stirring frequently. Stir in walnuts. Spread over crust.
Bake at 350 degrees F for 30 minutes. Cool on a wire rack.
Cut into squares; top with whipped topping.