Fried Green Tomatoes - I've shared this on both my visits.
A friend of mine is a big fan of the vegetarian restaurant Cafe Sunflower. When I told her I'd never tried it, she made a meal there happen for me very fast! We've met at the Buckhead location twice now for lunch and it definitely has some of the best vegetarian food around. The quinoa dish (photo below) was particularly outstanding and the fried green tomatoes are a must-try. There is a special vegan menu daily in addition to the regular all-vegetarian menu. They do have several dishes with tofu/seitan, which can actually taste very meaty.
Portabella Mushroom sandwich with baked sweet potato "fries" and salad.
Quinoa with greens and other tasty veggies - one of the vegan specials.