Tonton Streaming The Outer Limits (1995) S1E13 - Quality of Mercy

Major John Skokes is taken prisoner by the enemy during a savage galactic war and a seemingly undefeatable alien race. The tension increases when his cellmate, a cadet named Pri, is being transformed into one of them. Skokes must find an escape to save his cellmate and to avoid a disturbing revelation of the course of this war.