Cafe Sunflower is terrific.
Although a bit more Midtown and less Buckhead, Miller Union is a great hot spot with a fabulous veggie plate. The chef will definitely adapt for special requests too, in my experience. It's very farm-to-table and they showcase veggies nicely.
2140 Peachtree Rd NW Ste 105, Atlanta, GA 30309
999 Brady Ave Suite 106, Atlanta, GA 30318