If your Spanish is halting or nonexistent and you are heading south to Lima Peru Taste, defined as an annotated guide to Peruvian Restaurants might be the place to visit.
Their most recent entry La Gran Fruta is rated as Inexpensive and described as a "chain of small juguería (juice bar) and sanguchería
(sandwich restaurant) offers you a great variety of delicious fresh
fruit juices, as well as sandwiches, coffee, fruit salads and yogurt.They use local exotic fruits like aguaje, camu camu, cocona, granadilla, chirimoya, mango, lúcuma, maracuya, guanábana, papaya,
as well as other well known fruits like orange, pineapple, banana,
lime, melon, strawberries, avocado, tangerine, and peach among other,
alone or combined in different and delicious ways."
I will let you explore the rest of their picks.
Related: 2008 is the International Year of the Potato. Did you know?