This mission has you going near the heart of the Borg invasion force and defeating an Assimilated Gorn. (This is not as hard as it sounds). There is no transporter to the Sphere, you'll have to walk through the borgified trenches to the North of base camp to reach one of the a pillar consoles to summon one of the 12 Gorn Borg. You need to be in a team of at least three people to do so.
Once summoned, the Gorn will beam in close to the Console, but not directly near it (maybe ~10 m, so don't directly face the console or you'll get massively flanked). The Gorn will beam in with a small detachment of Tactical Drones for back up, but your primary concern should be the Gorn, as he has a Mortar on his bank that hurts. If you're at close range, he'll use standard Borg melee tactics, in addition to attempting to bite you. Once you've defeated him, return to base camp and retrieve your reward.
Also note that there is an accolade for defeating all 12 Gorn. If you're dead when the Gorn is defeated, you won't get credit for the kill. Vis-a-Vis, keep your team mates alive and res them when their down if you can.