Hanoi's vegetarian street food tradition predates modern veganism by centuries. Buddhist temple kitchens perfected phở chay and bún riêu chay long before the term "plant-based" entered global vocabulary, substituting shiitake and oyster mushrooms for beef stock, pressing tofu into sheets thin enough to mimic pork skin, and simmering tomato broth until it carries the umami depth travelers expect from bone broth. The Old Quarter's narrow lanes — Hàng Bạc, Hàng Gai, Hàng Đào — hold dozens of family stalls where a wok rings against blue flame at five in the morning and doesn't cool until midnight. A hanoi street food tour vegetarian walks the same routes as omnivore itineraries but veers into specialist kitchens: the vendor on Mã Mây whose bánh mì chay layers lemongrass tofu, pickled daikon, and cilantro into a baguette still warm from the oven; the corner stand on Lý Quốc Sư where bún chả chay substitutes grilled king oyster mushrooms for pork patties, charred over coconut husk coals until the edges caramelize. These are not compromise meals. They are parallel traditions, equally old, equally precise. Vietnamese vegetarian cuisine — ăn chay — observes the first and fifteenth days of the lunar month, when Buddhist practitioners abstain from meat. That bi-monthly rhythm has kept vegetarian technique sharp across generations. Cooks learned to coax texture from gluten, to ferment tofu into blocks dense enough to grill, to fold herbs into spring rolls so the mint and perilla carry the dish rather than the protein. The result is a repertoire that tastes neither Western nor reactionary but rooted in its own history. Guided vegan street food tours in Hanoi gather in the early evening, when the Old Quarter's motorbike traffic thins enough for walking but the vendors' grills are still live. A typical route covers four to six stops: a phở chay stall, a bánh cuốn stand rolling rice sheets around mushroom filling, a chè cart serving sweet mung bean soup with coconut milk, a bánh xèo kitchen flipping turmeric crepes. The guide translates menu boards, explains which herbs to wrap around which bites, and steers the group away from stalls that use fish sauce as a hidden base. Most tours finish near Hoàn Kiếm Lake, where the evening promenade begins and the city's public life unfolds under the banyan trees.