'RHOSLC' Star Jen Shah Eats 'Prison Sushi' with Inmates For Birthday Party

For Jen Shah, birthdays hit different in federal lockup ... because instead of going out for a fancy sushi dinner, she had to settle for the prison version of that delicacy.

Jen's good friend and former assistant, Murilo Bueno, tells TMZ ... the reality TV star's fellow inmates celebrated her October 4 birthday by making her "prison sushi" ... which consists of premade spring rolls wrapped in sticky rice.

We're told Jen's inmate friends at FPC Bryan in Texas asked her what she would do for her birthday if she wasn't behind bars, and when she told them she was craving sushi ... they did their best to make it happen, using whatever they could gather from the commissary.

Forget the raw fish -- they're not flying that stuff into federal prisons -- instead, her fellow inmates cooked sticky rice in hot water, wrapped that around those pre-made spring rolls and boom -- bootleg sushi roll!!! Yum?

We're also told Jen chowed down on prison-style quesadillas ... tortillas and cheese from the commissary grilled on a flat iron normally used to straighten hair.

For dessert, Jen's friend says they served "prison pineapple upside down cheesecake" ... which probably sounds better than it tastes. Murilo says a can of pineapples is involved, but she's unsure about the other ingredients. Use your imagination.

TMZ broke the story, Jen started serving her 6.5-year prison sentence back in February after pleading guilty to conspiracy to commit wire fraud. Her sentence has since been reduced by 1 year, and this is her first birthday behind bars.