Pixel Puzzles: UndeadZ

You get this achievement for killing a zombie with a grenade during a puzzle/zombie game. Just start any puzzle by choosing it and hitting the Go button. move your defender to the killing lane and wait for a zombie to appear. When it gets close, hit the Q button to throw a grenade, kill it, and the achievement should unlock.

Not sure what the 3 in the image is supposed to mean; I got it on the first kill.