On the corner of East Broadway and Forsyth, in Chinatown, there are some people selling a variety of foodstuffs. What I've been buying there is a sort of vegetable sandwich -- a regular, Western-style bun and stuffed inside something I take to be bok-choy flavored with some sort of mustard or horseradish. Is that what it is? Is it Chinese, or maybe Vietnamese? Can you get it anywhere else? It's delicious, and it costs only a dollar.