I had about 8 remaining feijoas after my friand experiment, so did I went where any self respecting foodie with a curiousity about obscure ingredients goes: Google.
I went out on a limb and tried "chocolate+feijoa"and found a blog with a section dedicated to feijoas. The chocolate feijoa cake took my fancy. I didn't quite have the required 1.5 cups of chopped feijoas, but substituted with about half a cup of milk to give it some more moisture.
It sunk a little in the middle, but who cares? The top was lovely and crunchy, and the centre seems very moist. I can't comment on the flavour yet; I'll let you know after I slice it up tomorrow at work.