An activity that requires little effort to finish; a job that's simple; easy.
When a task is easier to complete than previously expected, people will
sometimes use this phrase to express those sentiments.当一项任务比预期的更加简单时候，人们就会用 a piece of cake去形容；
The question is: Why? What makes cake "easy? Well, I doubt it's referring to the cooking process involved with baking a cake, because that requires a fair bit of work. 笨怀疑easy指的应该是烤面包的过程，但是这个过程也需要不小的精力。You have to crack eggs, mix stuff up in a bowl, set the temperature of the oven, and so on. 因为你需要去打鸡蛋，和面，设定温度等等。Alright, it's not that complicated, but it still requires effort.尽管不是很复杂，但依然很耗时，不是么。
Do you know what is easy though? Eating a baked cake! that's a pretty easy thing to do because it tastes good. 那什么才是简单的呢，当然是吃面包啦。Thus, this phrase may possibly get its "easy to accomplish" meaning from how simple it can be to eat a piece of this delicious desert. 所以这个俚语的来源很有可能指的就是品尝一块甜点是很简单的事情。However, that is simply a guess; the origins for this phrase are not certain.当然啦，这只是最合理的一个猜想，真正的来源还没有被证实。
1.英语很简单：English is just a piece of cake!英语不过是小菜一碟！
That's a piece of cake, just tell her you have been expecting to dine with her.
The approaching exam will be a piece of cake.