Grease and line a rectangular 16x26cm slice tin with baking paper. Preheat oven to 180 degrees (fan-forced 170 deg).
In a large mixing bowl combine all the ingredients (except chocolate), press into individual squares and press them randomly and firmly into the mixture in the tin.
Bake for 20-25 mins, but start checking early. The slice should be firm back after a light touch but still be a little wobbly and soft when it comes out of the oven. It will continue to cook as it cools.