In a large bowl, toss together the rolled oats, baking powder, coconut, flour and brown sugar.
Using your hands, rub the butter thoroughly through the dry ingredients.
Divide crumble mixture in half and press half into the bottom of the prepared baking pan.
Spread date mixture over the base.
Top with remaining crumb mixture, pressing together in clumps, in your hands, and then breaking it into small pieces, with your fingers, to scatter evenly over the date filling; press down lightly.
Place in pre-heated oven and bake for 40 minutes.