Lunch and Vivek go way back. Lunch used to run a diner until Vivek left him holding the bag when he betrayed Mech and Boss. Lunch turned that around in the end and is the drug trade himself. He gave Vivek his old 9mm in exchange an assassination job, never knowing what was inside it, a key. Lunch however did suspect he was up to something and had him followed. When Mech showed up he told him right where he would be.
Lunch and his ship, the Good Trip, have left Megaton in a hurry.