Pregnant Jamie Lynn Sigler -- Date Night with Lenny Dykstra's Son

With her baby bump under wraps, former "Sopranos" star Jamie Lynn Sigler left a dinner date in L.A. last night with the man responsible for her fetus ... Lenny Dykstra's son Cutter.

The 31-year-old actress just announced the pregnancy last week -- and confirmed the kid belongs to her 23-year-old fiance, who's a minor league baseball player.

Cutter Dykstra -- who was drafted in 2008 -- was clutching some cash on his way out of Craig's ... which is a good sign, considering there were rumors that his financial disaster of a father stole his $700,000 signing bonus. Cutter has previously claimed the rumors were completely false.