The CBD's recently opened Barrack Place precinct doesn't just offer Sydneysiders heaps of new coffee break options. It's also home to Chinese street food newbie Mo'st, which is slinging (what's said to be) the world's oldest sandwich.

Called rou jia mo ("meat sandwich"), this Chinese burger originated in the Shaanxi Province some 2300 years ago, during the Zhou Dynasty. Stewed pork belly is seasoned with over 20 spices, then shredded, mixed with coriander and capsicum and stuffed into mo — a flatbread that's typically baked in a clay oven.

Now, many varieties of rou jia mo are eaten all over China, and Mo'st offers seven varieties on its own menu. Fillings vary from the classic pork listed above ($10.8) to less authentic, more options. Think oven-grilled lamb patties with pickles and Greek yoghurt ($10.8); slow-cooked miso salmon with purple slaw and kimchi mayo ($14.8); and a vego option with tofu, king mushrooms, lotus root and sesame sauce ($9.8).

Apart from the namesake burger, the menu offers pork congee with preserved egg ($10.8) for breakfast, plus a Hainan-style chicken salad ($13.8) and handmade cold sesame noodles ($9.8) for lunch. For drinks, there's Five Senses coffees, Asian-inspired milkshakes and matcha concoctions on offer, too.