For the oat crust:
For the date filling:
1. Place dates, water and lemon juice in a small saucepan. Bring to a boil, stirring occasionally. Reduce the heat and simmer for 5-8 minutes, stirring occasionally, until the dates are soft. Remove from heat and add vanilla extract. Let cool to room temperature.
2. Preheat oven to 350F (175C). Line a 9-inch (23cm) square baking pan with a strip of parchment paper. Set aside.
3. Make the crust: In a large bowl, combine oats, flour, salt, brown sugar and baking soda. Add the butter and mix until crumbly.
4. Press 2/3 of the mixture into the bottom of the baking pan. Spread the filling over the base, Sprinkle the remaining oat mixture.
5. Bake for 25-30 minutes, until golden brown. Let cool completely, then refrigerate for at least one hour before cutting into squares.