Gwen Stefani -- Hollaback Mama ... Could Be Hottest Pregnant Chick Ever

A few times she's been around this track ... but she ain't no pregnant fat girl, she ain't no pregnant fat girl!

Gwen Stefani stepped out for lunch Friday in Beverly Hills at Mr. Chow ... and despite being several months pregnant -- with her third chld -- the singer still looked extremely do-able.

Hey baby, hey baby.