Preheat the oven to 180°C.
Lightly grease a baking tray with olive oil spray.
Sift the sugar, flour, cocoa and baking powder together in a bowl. Use a whisk, or a hand mixer on a low speed, to beat the apple sauce, egg whites and vanilla together.
Combine the egg white mixture into the flour until just mixed together. Do not over mix. Pour into the baking tray.
Using oven mitts, insert the baking tray into the roaster.
Close the lid set the timer and cook for 30 minutes or until cooked.
Allow to cool and sprinkle with icing sugar to serve.