To crush a Green Cube, you must make it fall from a considerable height, or crush it using a moving platform. There are a few opportunities to obtain this, but the first and most straightforward one that I found is located during Chapter 7.
After opening the four doors near the third reactor, enter the second one in the right. You'll see a tall column with a White Pad. Create a Green Cube. It will fall and break, and achievement unlocked.
Here's a video of the process.