Roast dinner - for a veggie.

My daughter is a vegetarian. My only experience of cooking a roast dinner for her, is if she comes for Christmas dinner, when I do all the traditional roast potatoes and vegetables. I do a duck breast for me and a quorn steak for her - cherry and red wine sauce for both. There will soon be an occasion for me to have to repeat the exercise, but I'd like to substitute something veggie for both the duck and quorn, so both are the same. Any ideas please?