He was Jason Garrett coach in NY and took the Giants to a Super Bowl using Garrett as a player QB coach. He was also the Giants Head coach that fired Sean Payton as OC (demoted from play calling) allowing him to go to the Dallas Cowboys to be reborn by the Tuna (Bill Parcells). Jason Garrett succeeded Sean Payton as OC of the Dallas Cowboys after Parcells left (Parcells went throughout the 2005 season without an official OC). Payton left and the rest is New Orleans Saints History.
So that is the Jim Fassel, Jason Garrett, and Sean Payton connection.