A Piece of Cake
This is a popular, commonly used expression to describe something that is easy or a task that requires little effort. The phrase originated from the earlier expression “cakewalk,” a 19th century African American tradition performed on plantations or get-togethers for freeman.
African American couples would walk in a procession or promenade around a cake and the couple deemed to be the most graceful would win the cake as a prize. The contest was not known to require a great deal of skill and the phrase was eventually adopted as boxing slang to connote an easily-won match.
Cake walks were later performed sardonically at minstrel shows by racist Caucasians imitating black culture in an offensive manner.
If something is ridiculously easy, this expression would be used. For instance, “compared to yesterday’s recipe, this fillet will be a piece of cake.” Other similar saying are “that was easy as pie” which also connotes a task of simplicity.
The first recorded usage of the term occurred in 1936, in a piece of literature by poet Ogden Nash, who wrote in Primrose Path that "Her picture's in the papers now, And life's a piece of cake."
This term also appeared in the famous song, “a Spoonful of Sugar” from the musical Mary Poppins. When you find the fun in a particular job, as the song says, “then every task you undertake becomes a piece of cake.”