In Chapter 34 of The Kingdoms, Kite goes on this musing about religion:
The golden dome of the cathedral at Cadiz showed, just. He had been trying not to stare at it as much as he'd been trying not to stare at the flagless masts of the Royal Sovereign. As of this morning, he hadn't been ashore for twenty months and two days. He had never wanted to with any particular exigency, but Cadiz was different. It wasn't home; he'd moved too often to have a home except wherever the majority of his clothes were, but it was a place he liked, and whenever he did look, he wondered if the same priests were there. He had started, since getting here, to want to go to a real Mass again, in a real church instead of the bleak grey English ones with their boneless English parsons. There was something off-putting about faith with no backbone and only just enough teeth to get through a cucumber sandwich.
Why is "cucumber" specified as the type of the sandwich here? I don't see any particular reason for it to have been chosen over any other kind of soft filling. I suspect that there may be some historical reason for the choice - the author sprinkles other little historical references around - but I don't know much about that time period at all.
As for what historical times might be relevant - Kite was born in the early 1770s a Catholic and essentially grew up sailing with first the Spanish navy and then the English one (as far as I can tell; multiple timelines partially told by flashbacks are confusing). He delivers this paragraph in 1805, shortly before the French change history to win Trafalgar. While both sides of the war have had access to information about the future for some years at this point, it wouldn't have been long enough for major cultural changes. I think, anyhow.
Why is a "cucumber sandwich" specifically used as what English faith has "only just enough teeth to get through"?