To unlock this trophy you must first recruit Mordin to your team, and complete the Horizon mission.
After you recruit Mordin, talk to him at every opportunity, and he will eventually bring up the topic of going to Tunchunka and helping a former colleague. The mission Mordin: Old Blood will be in your Journal.
This mission is pretty straight forward, and almost all enemies have armor. Since you must take Mordin, any other teammate which benefits taking out armor works well. You will mainly fight Krogan, crab animals, varren, and Vorcha.
To keep this solution as spoiler-free as possible, visit the Mass Effect wiki for this mission:
http://masseffect.wikia.com/wiki/Mordin:_Old_Blood.
For an Insanity playthrough, there is a renegade interrupt which makes a portion of this fight easier. There is also a paragon interrupt at the end, which benefits the story, if you have high enough paragon.
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