Se on helppo nakki. / This is a piece of cake.
While in English something is “a pice of cake”, in Finnish it’s an easy sausage (“nakki” is that kind of small hot dog or a frankfurter sausage, to be exact).
In English, you say “to make hay”, when you use an opportunity to get the most benefit. In Finnish, you say “helppoa kuin heinänteko” / “Easy as making hay.”