Very easy. Set up an Offline game on any map you like. Make sure to hit X in map selection so you can play on the large version (thus the enemy team will be more spread out) and set bots to Trivial. Change the player count to 8 so you have less enemies defending.
Start up the game. It's random in Assault whether you start as attackers or defenders. If you do start as defenders, quickly switch to the other team by
pressing Y before spawning, then selecting the other team.
Now, just use your best assault class to charge a base - you can scout out which one has low opposition before the game starts. Make sure your class has a Jammer beacon, it's invaluable for quickly attacking bases.
You just have to hack it, so stay near the CP even if you're being attacked. Achievement may take a few seconds to unlock.