Can be done solo (Instant Action) or in multiplayer (Ranked or Private match)
The achievement's desciption is pretty clear, and doesn't say anything about the difficulty. So, we're going to make it easy for ourselves. Any map is OK.
An easy method that worked for me was:
Settings: Nuclear Dawn map, Swarm combat mode, Trivial difficulty, 8 players, Friendly Fire OFF
Loadout: Guardian but equiped it with Assault Rifle as weapon 1 and Rocket Launcher as weapon 2. I also had the Repair Tool and the Det Packs.
I focussed mainly on hacking and capturing check points. The few bots that came to me trying to capture the control point were easy kills with the assault rifle since it was on trivial difficulty.
As soon as the DCM (Dynamic Combat Mission) became active, I focussed on doing those to increase the score quickly. If you have to do a DCM but there are too many enemies involved, stay away from it. Let your friendly bots do the job, and focus on another DCM if active, or otherwise capture control points if any available, or kill enemies one by one.
When hurt, heal using the repair tool!