You'll probably be able to get this by simply doing all the story mission and whatnot, but we will know you want that achievement now right? Right. To get this in 5 minutes just get in the saucer and just death ray EVERYTHING! Buildings, cars, people. A good technique is to destroy a building and then blast all the pitiful humans fleeing for their insignificant lives as it crumbles to the ground (whoops got a bit carried away there...)