@Xinjinmeng It's not the sandwich's fault it's delicious. =:) BLT's a classic, but adding even simple avocado boosts it to a surprising degree. And I'm not just saying that as an adoptive & exiled Californian. =:)
Bread: of the UK chains, I'd rate Gail's San Francisco style sourdough highest, via Ocado & Waitrose. (They make several others, apparently all commendable)