I’ve got to imagine it’s not ideal for making food even with long enough cooking implements because of the fumes. Sulphur not necessarily (idk what compound this would be, but we definitely eat sulphur containing foods), but there are all sorts of things that lava is off gassing.

If you were cooking something completely sealed, it might be okay, but it would have to maintain that seal with pretty extreme internal pressure, because of the huge temperature difference.