I’ve had experience of this mission a few times now, so if you find yourself struggling, here’s my tip: enter from the west. Still, it surprises me that even though I can’t kill anybody for this challenge, I’m allowed to bend the rules and call in rebels or use my AI team mates to kill people. Feels like cheating to me though.
“In Extreme difficulty and without killing any enemies, deploy to San Mateo Alpha then complete the mission ‘La Carcel Del Pueblo’.”