Hi, I know I have seen it before in Beijing on the food street near Wangfujing, but I don't remember the name - I think it has the 耳 character in it. It's not Shaanxi rou jia mo and it is definitely not Sichuan guo kui, but the bread used is similar. The vendor slices off some crispy pieces of pork and mixes them with lettuce and scoops it into the bread. At some point, hot pepper and sichuan pepper get added, but I don't remember that on the Beijing version - must be an adaptation to local taste.
Anyway, I saw it for the first time in Chengdu today, there were two of these carts by Computer City near XinNan Lu and the first ring...a very busy area for street food. Passersby were also wondering what it was.