Speak with Centurion Nivek, in the Northern Overwatch, to start this quest. This is a level 5 quest.

The Secret Life of Trees
It's tough keeping morale up here. After the massacre, the survivors held on - but barely. I've been doing my part by cooking up piglings - chops, bacon, roasts, and the like. This crazed Ghilliedhu, Vekas, keeps killing all the Piglings, thought! This post is miserable enough, but living without meat? No soldier should have to endure that. Kill Vekas and I'll use him to smoke the best rashers of bacon this side of Kaiator!
Head west and look for piglings clustered around a stand of trees. Vekas the Wicked has a thing for piglings, I guess. Let him pick on something his own size. Or at least something that's not a pig.

Centurion Nivek further warns you that Vekas is a powerful creature, and cunning. So be careful.

Click on "L" to open your quest log, then click on the current quest under "Story Quest", then click on "Vekas" to mark it on the minimap. Despite what Nivek told you, to head west, Vekas is actually to be found to the East. You will identify the mob by the red exclamation mark on his head.

Strategy for beating Vekas
Vekas is a boss monster, probably one of the toughest you've encountered on this island. It has more hitpoints, and inflicts more damage. If you are playing a fragile class such as a sorcerer, facing him head on could mean suicide. The correct way to beat Vekas is to use a hit and run strategy. Use your attacks from a distance (or from melee, depending on class), and as soon as Vekas is performing his own attack, step back out of his melee range. Keep doing so until you've exhausted the enemy's health. This might take some practice, but it's a useful strategy for killing similar monsters, that are slow but hard hitting.

After you kill Vekas, the quest tracker updates to: "Tim BERRR! Time to make Nivek's day". Go back to Nivek at the Northern Overwatch. He congratulates you on a battle well fought. It might not seem like much, but armies depend on their stomachs for more than just traveling.

Your reward includes Nivek's Slippers for Sorcerers, Priests and Mystics, Nivek's Best Bots for Archers, Slayers and Warriors, and Nivek's Sturdy Footwear for Berserkers and Lancers.

You also get the following achievement:

Timber!
Completed "The Secret Life of Trees" Quest