Ja Rule -- SPILLIN' PRISON SECRETS

Ja Rule is breaking the incarceration code of silence ... revealing something only the people inside his penitentiary have known about ... HIS SECRET RECIPE FOR PRISON CHICKEN CURRY!!

The rapper -- who recently told us that he cooked like a maniac during his 2-year stint at Ray Brook Federal Prison -- appeared on "TMZ Live" moments ago and explained how he transitioned into a locked up Chef Boyardee.

So, if you plan on doing time in the near future, listen up ... 'cause Ja has the PERFECT recipe to slam together a nice chicken dish in the comfort of your own cell.

... and it actually sounds pretty damn good!!

Check out the clip.