Thank you, It is easier to understand why "go" is needed in the sentence if you translate it that way... "What reason is it that the food is on the plate? "
It has to do with whether you have a direct relative clause ("The direct relative particle a requires the autonomous verb form") or an indirect relative clause ("The indirect relative particle a/go/ar and nach/nár requires the dependent verb form").
I wrote a bhfuil first time round because a) it's what I heard and b) it's standard in the west and the north. But, it was a listening exercise, so I listened again. And again. And again. OK, Duo, fair cop . She does use the Munster go bhfuil. But you have to admit, dear Owl, that it sounds very ghoulish.