I use Hills Science Diet, they do a range of different foods for sensitive dogs, puppies, adults, senior etc.
I was told from our vets to mix in boiled brocolli and cauliflower, this fills them up and doesn't make them bloated. I often boil some chicken up with rice too.
I've just checked this webiste http://www.hillspet.com/index.jsp
they do vegetarian food still.
Good luck with it. Also your vet should be able to suggest something.