Avatar: The Last Airbender

Avatar: The Last Airbender (also known as Avatar: The Legend of Aang in the UK) is an American animated series produced for Nickelodeon. It follows the adventures of a young monk with special elemental powers, Aang, and his friends as they battle to save the world from a conquering militant nation.

City of Walls and Secrets (Season 2, Episode 4)
A "freedom fighter", Jet, is taken prisoner by the police force of Ba Sing Se and subjected to brainwashing.

Lake Laogai (Season 2, Episode 37)
It is revealed that the group's guide to the city, Joo Dee, is a brainwashed slave of the corrupt official ruling the city. Jet's brainwashing is revisted, and both are triggered with the phrase "the Earth King invites you to Lake Laogai".