The Shield Rush ability is unlocked via the Abilities menu, which is accessible from any Control Point. The ability you need is "Shield Rush
", but "Shield Rush 1" will also make this easier.
To use the ability, you need to hold
to dash when in close contact with an enemy (it is also possible to do while levitating, but a lot more difficult).
You will come across plenty of enemies as you progress through "The Foundation" DLC. However if, like me, you've found yourself short upon completion of the game, I found the best place to accumulate kills was around the Control Point at Maintenance > NSC Power Plant
This area is frequently populated with low-level enemies that can be killed with one hit of "Shield Rush 1", and I was able to kill approximately 10 enemies with every visit. Simply kill the enemies, travel to another Control Point and travel back to NSC Power Planet and repeat until the achievement unlocks.