In the Space Frontier booth, you will come to the Terraformal Event. Recommend this is done if Free play. This is an annoying and luck based achievement. The luck part is that you do not always get a TNT Powerup. You will need to do a few things to prepare the area for Terraforming before the TNT Powerup appears.
You will notice a number of targets that are attached to the tops of mountains. When the target is hit once, it will transform into two targets each, when those two are hit, it will make a tree. That means it has Terraformed.
What you need to do is hit all the single targets, so that's left are just the set of two targets each. Now that you have all the targets siting in groups of twos, its time to sit and wait for the TNT Powerup to show its self. If its not the TNT Powerup, then restart the level (if you are doing this on Free Play) and try again.