I would consider Collins to be more of a bar than a restaurant, unless you want a bunch of fried vegetables and other foods! Flagstaff Brewing Company is quite close to Collins and their burgers are great - if you can snag a seat on the outdoor patio, it's some great people watching too. Beaver Street Brewery is also known for their burgers - it's a little south of the downtown area where Collins and Flag Brew are (but still within walking distance) so you don't quite have the same atmosphere.
Flagstaff Brewing Company
16 East Rt 66, Flagstaff, AZ
Beaver Street Brewery
11 S Beaver St Ste 1, Flagstaff, AZ 86001