“小菜一碟”用英语怎么说

1.up in the air:

What's going to happen isn't decided yet; something is uncertain;

e.g. I'm not sure where I'm going to live in the future. It's still up in the air.

2.a piece of cake:

e.g. After learning these 10 IELTS idoms, getting a high score in IELTS is a piece o cake.