This requires you to research and build 3 Gob-O-Bots. That is assuming you don't lose the initial 2 you're given at the start of the level.
To research the bots you will have to research your way through the tree and research the guard post and workshop beforehand. You're also going to need some evil so build a smallish army, and capture the northern evil island from the enemy. I recommend this spot as this is where the first food delivery will pass and will make killing it easier as there will be less enemies to encounter.
Once you can research the Gob-O-Bot, do so and build 3 of them. When you have a total of 5 the achievement will pop.