This was recently mentioned in a couple of posts - some people finding it at, of all places, a Chinese restaurant... given that it's a British (or Scottish, can't remember) invention.
Anyway, if you're into this dish (can't say I am...), one of the best kept secrets in the city for it is British Style Fish and Chips. It's not on the menu, but if you ask, the owner will make it for you. Also, may I also say that this place is HANDS DOWN NO CONTEST the best Fish and Chip shop in Toronto. It shames every other piece of fish I've tried by a long shot. Hope you enjoy, whether it be the fried Mars bar or the F+C (or both! eek!).