Preheat oven to 350° F. Grease a 13-in by 9-in baking pan, set aside.
In a large bowl, combine the flour, crushed walnuts, oats, brown sugar, cinnamon, baking soda, and salt. Cut in the cold butter until crumbly.
In a medium-sized bowl, whisk together the eggs and brown sugar until well blended, and close to the ribbon stage. Add vanilla, stirring to combine. Fold in the chopped dates.
Press ¾ of the crust mixture into the prepared pan. Pour the filling over the first crust layer, making sure to spread evenly over the entire surface. Add the ½ cup of chopped walnuts to the remaining crust mixture. Evenly distribute the last of the crust mixture over the filling.
Bake for 30-35 minutes, until lightly browned and a toothpick inserted into the center comes out clean. Cool completely on a wire rack before cutting into squares.
Store in an airtight container for up to one week. For longer shelf-life, store in the refrigerator.
Crust can be made in a food processor, but be careful not to over-mix.