Jennifer Love Hewitt and Fiance in Photog Scuffle -- Criminal Investigation

Jennifer Love Hewitt and fiance Brian Hallisay were involved in a pasta-fueled confrontation with a photog Friday night ... and cops have launched a criminal investigation.

JLH and Brian were leaving the always-delicious Toscana restaurant in Brentwood when a pesky paparazzo prepared to snap some pics. We're told the couple asked the photog to lay off, but he ignored them and started snapping away.

Hallisay then allegedly got into it with the cameraman, and during the scuffle the photog claims the camera hit him in the face -- near his eye.

Apparently Jen -- who is pregnant -- felt so bad she let the photog snap a few more pics ... and then she and Hallisay left.

Unlike Toscana's rigatoni, the confrontation didn't go down well with the photog, because law enforcement sources tell us he went to the cop shop a few hours later and filed a battery report against Hallisay. Our sources say when he came to the station there was no visible injury to his face or eye.