This is story related and can't be missed. the achievement is called Thunderstruck.
this is a boss fight against a Cat-G akrid. by this point you should be used to scanning new akrid as you come across the, so after scanning the boss, he attacks at random with claws, mouth and egg pods, so proceed to dodge (A button) his left claw, right claw and mouth smash attacks, if/when he shoots the egg pods take them out quickly with the shotgun before they hatch then focus on shooting his head till it cracks and dodging. this method works for the previous 2 fights against him as well.
for the last part after reaching your mech rig again. block with (RB) when prompted then LB to grab it then mash the A button and then hold right trigger after his tongue attack. after about 3 drill attacks to the head he should go down.