You can steam syrup sponge in a pyrex bowl. Is it plain cake? So syrup or jam in bottom of bowl, mixture on top, cover top with greaseproof paper, and steam (for a long time, if memory serves!) Chocolate could be steamed with nutella or similar at the bottom?
You can microwave cake, but I think its best eaten straight away.
Oven isn't something silly like off at the mains? or timer button been knocked on???
My mom used to microwave little cakes when I was little.
I still shudder at the memory
My suggestion would be to freeze the uncooked batter for another day and make some kind of rocky road/fridge cake if you have the ingredients. open a pack of biscuits or do a mad dash to the supermarket for cake