Preheat the oven to 190 degrees C. Grease a 20x30cm pan.
In a large bowl, mix together oats, cake mix and melted margarine so that it makes nice clumps and there is no dry mix left. Press 1/2 of the oats mixture evenly into the bottom the prepared pan. In a separate bowl, mix jam with water then spread over the crust. Sprinkle the remaining oat mixture evenly over the top.
Bake in the preheated oven for 18 to 23 minutes, or until the top is lightly browned. Cool before cutting into bars.