McStroke Family Guy : Season 6 Episode 8

Peter decides to grow a mustache, and after being mistaken for a fireman, ends up lending a hand when a fire breaks out at a local fast food restaurant. The owner gives him unlimited burgers as a thank you, but he eats too many and has a stroke. When Peter recovers, he vows to expose the fast-food company for what it really is, becoming friends with a genetically engineered cow along the way.