Nice.
I did the non-oven version tonight. It is definitely lacking substance, and I thought it tasted raw to start with (but after than the garlic and stuff shut down my critical faculties). I think it has to be either oven baked or the onions/garlic fried to start with. (So far as possible I used the very same ingredients/quantities as the first go).
Pro tip for the sandwich: yon chappy uses a wire tray to enable buttering (sorry, 'mayoing') of both side. I've setting on just doing one side, then once it's nicely toasting in the pan, doing the other before the flip. Much less messy.
As previously mentioned, seconds were required for the sandwich (the loaf I used is smaller than normal, so it a) fits two in a pan, and b) fits the cheese slice exactly). I figured I could pre-cook them then when we actually wanted them give them 30 secs or so in the microwave to get them pooling again. Well, that works but the bread gets to be too soggy to cut, and the cheese can be VERY hot indeed. I tried pre-cutting too, which was better, but still soggy. The solution I found worked best was to pre-cook and then serve cold when required. The bread is again not crisp, although not actually soggy, but the major difference is that the cheese is much more tasty! And the heat contrast is good too.