<<Disclaimer: Verify this information before applying it to your situation.>>

Elizabeth,
The only suggestion I can make is to try to have fresh salads; almost every
restaurant has a plain green side salad.  Take your own dressing in a
convenient pack in your purse. You can always eat more later.  If the
potential employer asks about it say something to the effect that a big
lunch slows you down and you want to be on your toes for this interview.
They'll be impressed and you'll be safe.
Good luck,
Jeny