It was an episode which Bart was a ninja who handed out flyers for a Chinese takeout restaurant. I don’t remember too much else about it. What was it?
Episode entitled “Lisa the Tree Hugger”, from Season 12. Bart becoming a menu ninja was only a subplot to lead into Lisa’s environmentalism.
Joshua Jackson was the guest star, he played an environmentalist radical type, and Lisa had a crush on him. She was sent to live in and protect a redwood, the oldest tree in Springfield. It was struck down by lightning while she was supposed to be in it and she was presumed dead. Hilarity ensues.