茶餐廳 is cha chaan teng, a Hong Kong-style diner. Much like traditional US diners, they serve a variety of sweet and savory breakfast items alongside hearty, simple food you might associate more with lunch and dinner. Typical items for a cha chaan teng are toast with a sweet topping; noodle soups (often made with instant noodles) containing spam, chicken wings or hot dogs; fried noodle dishes; stir-fried or deep-fried dishes served over rice; and Western-style food like spaghetti with meat sauce and meat in cheesy or creamy sauces.
Cafe de Lulu got some posts here when it first opened last year, but I never made it down there- something about eating in a windowless basement seemed unappealing even when I wanted to check out the food. I finally made it there recently and it's the most charming basement diner I can imagine. A very friendly proprietress will chat with you in English, Cantonese or Mandarin and the semi-open kitchen allows the short-order stirfry chef to wander around and say hello. The decor is ikea-style and it's easy to forget you can't actually see outside. Several flat panels show Chinese (Mandarin) TV.
Aside from it being one of the few places anywhere in Boston to get the full selection of traditional short-order breakfast all day items, the notable feature is 3 dishes with rice and (basic watery) soup for $22. You select from about 75 items ranging from sweet and sour pork (HK style, not the puffy American kind, and the best version I've had in the US) to a delicately flavored homestyle eggplant and fish filet stir-fry, to salt and pepper deep-fried shrimp, to various combinations of mushroom and vegetable.
The room maybe isn't dirty enough and the service isn't gruff enough... but otherwise this is as authentic of a Hong Kong diner experience as I suspect you'll find most places in the US.