Mass Effect Legendary Edition

To get this you need to destroy the shields of 25 enemies using the Overload ability. Basically you (or a squadmate) need to cast Overload on a enemy with shields (blue bar over their health indicator) and successfully destroy the shields (deplete that bar) - it does not count if you merely damage the barriers but do not fully deplete them. On easier difficulties an Overload will destroy most enemy shield defences in one hit, but if you're playing on Hardcore or Insanity you will want to whittle the shields down to about 25% through other means before casting Overload.

You don't need to do it with your own character, you can direct a squadmate to do it - in this case the easiest squadmate to use is Miranda, as she has Overload (and Warp) and is available from the start. Other characters who can learn Overload are Garrus, Kasumi, and Wilson. Shepard can learn this power if made an Engineer or a Sentinel.

The enemies that most often have shields are enemy mechs and engineers, especially the Eclipse ones (yellow armor), or the geth (especially on Hardcore and Insanity).

To do this reliably you can find a group of Shield-equipped enemies (usually the Eclipse engineers or geth), destroy as many Shields using Overload as possible, and then reload the save and do it again until you have 25. If you are playing on higher difficulties every single enemy you encounter during Tali's recruitment mission on Haelstrom and loyalty mission (as well as Legion's loyalty mission) will have shields, so make sure you bring along a character who has Overload (neither Tali nor Legion have it).

An easy way to unlock this early is in the mission Dossier: The Convict where you rescue Jack. Just before the end of the mission, a bunch of Blue Sun enemies you have to kill will have shields, just continuously use Overload on them until the cheevo pops. Die or reload save and keep doing it until it unlocks.