Override: Mech City Brawl

To perform a Counter-attack you need to hold Y to shield yourself and either press LB / LT / RB / RT before the enemy hits you to counter it.

The easiest way to do this is on the Campaign (Arcade mode). You will meet Xenotypes looking like the Xenomorph from Alien. These low-class monsters will dash at you then use 2 punches, simply try to counter the dash (it needs timing) or back down a little and counter the double hit.

You will need multiple missions to get the achievement as the counter deals 30 damage, which is enough to one shot the first monsters.

Note that the range type monsters (those firing green goo) won't melee you, this is why the Xenomorphs or Heavy-plated ones are the best.

Edit : I wanted to be sure about it before including it. But you can chain the first campaign mission to complete it quicker. Simply start a new campaign, counter-attack to kill all Xenotypes, then leave and delete the save. Create a new campaign and you should have around 15 monsters each to complete the 30 counter-attack cheevo