Kill Doctor Maleficus and obtain the Doctor's Key. Use the key to open the Doctor's Strongbox to retrieve The Art of Fel Reaver Maintenance and deliver the book to Nakansi at Invasion Point Cataclysm.
The best way to destroy the rest of the Legion's supplies is to use their own weapons against them. I've been working on a rig that will let you take control of one of those Fel Reaver Sentinels below.
There are a couple things I need to work out, yet. For that, I'll need the manual that Doctor Maleficus keeps locked in a chest near the bottom of the ramp. He probably won't give up the key without a fight, so you'll need to capture it. Bring the fel reaver manual back to me and I'll do the rest.