I think the question should be, "what did you eat last?". The word "last" comes last :)

Totally agree with Nicole. Both are correct.

I just had broiled ribs.

@nacir: what did you eat last or what did you last eat are both gramarically correct. Just because the word last is there, it doesn't automatically mean that it's more correct if it's placed towards the end of the question. :-)

Sophia I had a pretzel bacon burger from Wendy's! Lol.

Hi Sophia, it's the second one. :-)