Overcooked! 2

You have to get 3 stars in the 6 levels of the world 3. You don't need to do the Kevin's levels.

Here is a playlist containing videos of all levels unlocked in 4 stars duo mode. They will show you the technique to use, but you just have to make 3 stars for this achievement.
https://www.youtube.com/playlist?list=PLTg8yNY-9NDMNpQs1RLGR...

See also below the 6 levels separately. Good game.

Level 3-1 : Level 3-2 : Level 3-3 : Level 3-4 : Level 3-5 : Level 3-6 :

Here's a youtube walkthrough and tips of it. Please enjoy it.