I just did this last night, so I don't know if the recent patch changed anything from what it was previously.
On the 'non-lava' side, there are two ground 'click plates'.
One is at '9 o'clock' on the circle on the ground, one is closer to the locked gate (around where the barrels are.. you may need to destroy/move the barrels... possible dig to uncover it).
There are a few traps around you might have to disable/set off to uncover both click plates.
Standing on those will turn off the lava on the other side, which will allow access to the lever before the gate on the lava side.
Pulling that lever opens the gate on the non-lava side, which allows access to the lever behind that gate.
Throwing *that* lever opens the gate before the chest.
Hope that's not too confusing.
It's kind of a lot of moving back and forth.
I had 4 in my party and had everyone 'disconnected' so I could move them independently to do it.
You can probably do it with 3 people, but you might need a barrel or two for the click plates.
Last edited by Pubknight; 11/12/15 02:54 PM.