Body lock triangle (figure four) escape from the back.
The key here is to take opponents strong body triangle, make it weak, and escape the weak body triangle. Throughout the escape, priority should be given to controlling the choking arm.
Back escape when you fall to opponents control arm side.
In this video, I also explain how the bottom guy can choose what side to fall to.
Escaping the back when you fall to opponents choking arm (as opposed to his control arm).
The big concern here is a threat of potential arm triangle choke (aka head and arm choke).