Start heating your oven to 200 C / 400 F / Gas Mark 6.
Zest the orange; set the zest aside. Put the orange in the fridge for another use.
Put the flour and the butter in the bowl of a food processor and whiz a bit until it looks like crumbs, then whiz in the brown sugar.
Scoop out 1/3 of this mixture and set aside.
Now to the mixture in the bowl add 2 or 3 tablespoons of water a tablespoon a time, whizzing a bit after each addition. Stop when you've added enough water to make it come together as a dough.
Make a layer with the dough in the bottom of the baking pan, poke it all over with a fork, then pop in the oven to bake it a bit for 10 minutes.
While it's baking, add the apricots to the food processor bowl (don't worry about rinsing it out first) and whiz a bit to chop them up. Pop them into a bowl, then mix in the raisins and the orange zest, then the jam.
In a separate bowl, put the reserved dough and the oats, along with a teaspoon of water, and rub the mixture roughly with your hands so that it becomes a coarse crumble.
When the bottom crust has had its ten minutes, remove it from the oven and spread the apricot mixture evenly on top. Sprinkle the oat crumble evenly over top, then pop back in the oven for 20 minutes or until top is lightly golden brown.
Use a baking pan that is 9 x 12 x 2 inches (22 x 30 x 5 cm). Or, you can use a smaller pan, and aim for thicker squares.