Bill Clinton -- I'm at a Crossroads with Sean Penn

Bill Clinton and Sean Penn came face-to-face in Hollywood last night ... but there was no real beef ... because they were eating at a vegan restaurant.

Clinton -- with a full secret service escort -- hit up Crossroads restaurant ... to meet Penn for a meat-free dinner date (Bill is a vegan these days).

Unclear why they got together -- Haiti? Global human rights? Charlize Theron?

All we know is the two have known each other for years ... and even appeared in a "Funny or Die" video together back in 2011.