duck soup
An easily accomplished task or assignment, a cinch to succeed, as in Fixing this car is going to be duck soup. This expression gained currency as the title of a hilarious popular movie by the Marx Brothers (1933). The original allusion has been lost. [Early 1900s]
http://www.answers.com/topic/duck-soup
Good luck
This is just my belief of where it comes from... I really don't know if it's true, but it's an extension of the old saw, "Shooting ducks in a barrel."
Think about it... You're right next to the barrel, and open up on a duck with a 12ga shotgun... What do you wind up with? "Duck Soup!"
Mark (Nasty, but that's what I think)