'Mighty Ducks' Goalie Shaun Weiss

Shaun Weiss, the goalie in the 'Mighty Ducks' movies, got all nostalgic celebrating his graduation from a drug court program ... chowing down at a diner that's special to him.

Just days after getting his certificate of completion from the D.A.'s Office in Yuba County, CA ... we're told Shaun and his good friend, Drew Gallagher, hit up the super-popular Brent's Deli in the San Fernando Valley.

Why there? Well, for starters the pastrami is to die for ... but also, we're told the deli's the first place Shaun went when he was released from jail in August 2017 during one of the worst points in his life.

Shaun's had several stints in jail after that, but in going back now, he wanted to reminisce on…