Popular banh mi. They do a "traditional" version for 15,000d which delicious and is a great price for a tourist spot. Their special (Phi Banh Mi Sandwich) is 35,000d and comes with avocado, laughing cow cheese and other ingredients not in the traditional version. Both are quite spicy which I loved but you should ask for less chilli if you don't like spice.
They also do a vegetarian version for 25,000d and you can add avocado to any sandwich for 5,000d.