AFAIK all the veggie burgers are the same? Gardenburger Malibu burgers. They are the "veggie-filled" type, not the "meat-like" type. Just about anywhere that has burgers has them. I'll be honest--I love veggie burgers that are filled with veggies and I LOVE French fries, so I eat a lot of the burgers and don't mind. But there aren't always a lot of other QS options. I've also had the vegetarian tacos at El Pirata y el Perico, the veggie sandwich at Studios Catering Co (which was good but very flat, I think they use a grill press?), pizza at Pizzafari (which comes w/ Caesar salad which is not vegetarian), the Picnic in the Park at AK (now seasonal), there's a few options at Sunshine Seasons, someone already mentioned the Lighthouse sandwich ... basically every restaurant, QS or TS, will have at least one option, and most TS restaurants also have at least 1 other dish that can be made vegetarian (like at Sci-Fi, besides the tofu, you can also get the shrimp pasta without the shrimp, or a veggie burger). So I would say overall, if you are a vegetarian who is basically not picky (other than not eating meat, of course), there is always plenty to eat and you should choose based on what type of food you like and not by specific menu options.
By the way, Jiko, Boma, and Sanaa are all AWESOME for vegetarians, and The Mara doesn't have a huge vegetarian selection but their falafel is the best I've ever had. So we loved our stay at AKL last week.