I was referring to pho specifically. But in general, vegetables are harder to find if you are away from the tourist areas. I traveled the entire length of the country, over 2000 miles on a motorcycle, from the Cambodian border to the south, to the "North Pole" (border with China). If you saw a menu, then you ate at touristy places.

At one point, while in the extreme north, I might have eaten dog once or twice. Who knows? No one spoke English and Vietnamese is a very difficult language. Of course, no menus.