This restaurant has been around forever. Owned by Mercedes herself who's a very nice old lady. For lunch they serve a menu, which is about 6 or 7 soles and the place gets packed with locals. At night she's there and will cook for you if you want, but I never found anybody there at night when I went. Veggies are fresh and food very good! I'm a vegan and even though they've offered to substitute something non vegan for something else a couple of times, the waiters have also told me that there certainly wasn't cheese where there was, so you can't be picky here.
Cons: Service is bad in rush hours!