Thought I'd poke around online and see what I could find.
Red Robin, interestingly enough, not only doesn't post nutrition info on their website, but there doesn't seem to be nutrition info listed for them anywhere else, either. So, instead,
here's a nutritional listing of a beef burger with swiss cheese and portabello mushrooms, with mayo and bun, from Ruby Tuesdays. Obviously, having just the burger and cheese would minimize some of the calories and fat...but it's still going to be through the roof.
Here's the same sandwich, just with a turkey burger instead of beef. Notice it's less fat and less calories, but not by a huge amount.
Not to sound all "holier-than-thou," though! I had one of their burgers with cheese
and bacon on Saturday!

That's a once in a major while treat for me, though. Interestingly, I couldn't finish it and it made DH (who had the same thing) and I both so full we didn't eat dinner!
Just stuff to ponder. I know I was totally, totally shocked to find out how many calories (and worse, how much fat) was in restaurant burgers. They are just mind blowing!