Taken from Steam guide:
Map: Small, no empires, no primitives, maximum planets, 1 FE, no crisis or marauders
Government/Ethics: Whatever is easier for you (not pacifist)
This can be a fairly difficult achievement. For this one set up a small map with 1 FE. After colonizing the galaxy, take it easy and focus on building up and researching repeatables. Once you pass the date you set for late game, release some uplifted primitives as vassals, some FE's wont awaken with only the player empire on the field.
Once they awaken, declare war and let them take a few worlds. Watch their fleets for a Titan, they will sometimes only build them during war. Once you see it, send your fleets in and take it out. It will likely escape a few times before going down, but stay strong.