wow! this is really smart - I always wonder how can I still make a sandwich now that I stopped eating bread. that is a great idea :)
I guess one can do a similar thing with a bell pepper (there would be different ingredients for stuffing, since it has more robust flavor) also, I just realized I recently tried a "rice burger" - it had veggies for the main part, but the neat thing was that it had too slices of sticky rice fried in a way that let them hold the sandwich together.
it was nice, still I prefer this cucumber version.