Neither a dish nor a metaphor. It seems to be quite literal.
The hot burning flesh refers to a living human being—or some part thereof.
The food referenced will be more familiar in Great Britain than the U.S.
It’s from a book called A Beginner’s Guide to Being Mental, by Natasha Devon. Although this selection verges on being soft-core porn, the book overall is a self-help book on mental illness. The quote is about anorexia.