Did the sandwich originate in China? Will we ever know? My bets are on yes to both.
Would I eat a donkey burger? I do not know. Donkey lard, well, bleh, but I am not ashamed to eat pig. Does that make me a hypocrite? Yes. Were I in China, I would most likely do as I try my best to do, eat what is served.
Lucky Peach guide to Chinese sandwiches
DONKEY BURGER
驴肉火烧 LU ROU HUO SHAO
Two towns, Baoding and Hejian, claim to be the home of the donkey burger, but they differ mainly in the shape of the bun: a light griddle-toasted flatbread that gets its flaky texture from donkey lard. Baoding’s are round, while Hejian’s are rectangular, but the middle of both is all donkey (and maybe a diced green pepper). The donkey tastes like corned beef. The popularity of the sandwich might explain the local idiom in Hebei Province: “In heaven there is dragon meat, on earth there is donkey meat.”
The Lunch Encounter 