First off, I strongly suggest you play through each booth in Free Play (after getting your co-op achievement out of the way...) as you have the ability to restart any minigame.
Each shooting gallery gives you 2 power ups. One before and one after the pies are thrown at you. It seems the 2nd one is the random one and more commonly the 1st power up is the same each time you replay the level. I suggest using the Terraformal Event
minigame in the Space Frontier booth as there is an achievement you need this power up for here as well:
Either follow the guide there or do the following:
Once the level starts you see there are many single targets on the mountain that you can throw rings on. Throwing a ring on them opens a further 2 targets each. Ringing those 2 targets turns the whole thing into a tree. What the achievement wants is all of the trees to be spawned at once. The only way to do this is with TNT.
To prep the level for terraforming we need to get rings on each target on the mountain - to the point where there are now 2 targets on each that need activating. Once you have that done you must wait until the power ups come. If you don't get the TNT after the pies come at you, restart the level and proceed to set up everything again.
Once you do get the TNT power up simply activate it by pressing
to detonate all objects on screen. This will pop both the achievement for using the TNT as well as the achievement for Terraforming all the terrain at the same time.
If this is troublesome and you want the achievement faster, you can get the TNT achievement in the Invasion of the Space Raiders
minigame in the Space Frontier booth with very little effort.