Hue is known for being the most culturally Buddhist city in Vietnam, which means it has (in my opinion) some of the best vegetarian food in the world.
Of all the vegetarian restaurants in Hue, Lien Hoa (3 Lê Qúy Dôn Street) is definitely the most popular and well-known among tourists, expats, and even locals. It’s a good place to bring big groups, since many of the dishes are served family-style, and you’re guaranteed to never break the bank when you split the bill (around 20,000-50,000 vnd a person.) Personally though, I like the cheaper, more local, vegetarian options when I’m eating solo or with a few friends. I’ll introduce you to those places soon enough.