Wanting a completely vegetarian lizard narrows things down a bit. As SnowSnake suggested a Uromastyx would be a good choice, also a desert iguana I think could meet your needs. It is smaller than a green iguana staying between 14-18".
Type in vegetarian lizard in search engines and read up on a few care sheets.
Keeper of 5 snakes, leopard geckos, 1 green iguana, 20+ tarantulas, 2 dogs & a bunch of rats!