Preheat the oven to 350 °F (180 °C) and prepare a baking dish.
Make the date filling by boiling dates, water, lemon juice, and brown sugar, then let it cool.
Prepare the crisp mixture by combining oats, flour, brown sugar, and baking powder, then add butter and mix.
Layer half of the crisp mixture in the baking dish, top with the date filling, then cover with the remaining crisp mixture.
Bake for 55 minutes until golden brown, then cool, unmould, and cut into squares.
