Yeah, my oldest daughter went to Peru last year. She's lacto-ovo, and was with a group doing medical work and they were all able to get vegetarian meals though I'm not sure how far ahead they had to schedule their requests.
Lima has a bunch of vegetarian restaurants. Unfortunately I don't have the guide book in front of me. Some are Indian and Chinese. Maybe a Google search or something?
Cusco has several as well. My daughter's group went to two of them, I don't have addresses either, but found the website for one of them: Moni Cafe. It had traditional Peru food rather than "salads and sprouts" according to my daughter.
This is theirwebsite
, sounds very nice. Wow.
There are also lots of familiar chain restaurants in the large cities; Chilis, Pizza Hut, Applebees, Taco-(something?), Denneys, McDonalds where you can get something moderately vegetarian just as easily as you can here. While you may hate McDonalds or whatever, at least you know they serve salads or shakes or something familier if there's nothing else handy.
In the smaller towns, you'll need a reliable translator or a good grasp of the language to get the message across, but once they understand, people are usually very accomadating. As Froggy mentioned, Fried Plantains are very common - like a starchy potato for breakfast and even dinner too. One good thing, they usually use corn or other vegetable oils for frying as animal products are expensive and they tend to use them only on more fancy occassions/recipes.
There is one place I can recommend specifically because my daughter kept the menu: It's an all vegetarian place called Comedor Vegetariano Delta
located at Lake Titicaca (which is one place you absolutely MUST go!!) Don't have a website or anything but there's not much else around there. They have (well, had) a Quinoa Soup that my daughter STILL raves about.
And I just looked; Happy Cow has a whole page devoted to Peru's
Vegetarian restaurants. That should help too.