I agree with all of Crockett67's recommendations, especially NorthStar. The one place close to campus I can recommend is a Korean restaurant called Diaspora. It even has a surprisingly pleasant atmosphere for a campus ethnic restaurant. But the best food in Columbus is not near campus. Hope you have a good visit.
Campus is hard, not for vegetarian food. You can always find something around here. But it's a large campus... and while there is great food there. It's closer to Fast Food / Pizza / Ethnic just due to location. Here's what's off the top of my head
Aladdin's Eatery - Mediterranean
2931 N. High St.
Betty's Fine Food and Spirits
680 N High Street
Columbus, Ohio 43215
Blue Nile - An Ethiopian restaurant
2361 N High St
Columbus, Ohio 43202
Northstar Cafe - Always packed but soooo good!
951 N. High St.