It's a piece of cake 轻而易举，小菜一碟

【例句】 　
Once I've done that, it's a piece of cake. 　　
一旦你做到了这一点，接下来的事情就是小菜一碟。

I think it's a piece of cake for me.
我认为对我来讲是小菜一碟。