I prepared this delicious sauce and it was given to me by a friend who was married to a Peruvian in Los Angeles, Ca, I also would like to mention that not only El pollo Inca is good but el pollo a la brasa from Los Angeles by at 91 west fwy is 100% rico. The sauce is:

2 tablespoon mayonnaise
lemon juice
ground cumin
garlic
olive oil
a bunch of cilantro
onion
Serrano chiles
salt and whole pepper

Grind all and enjoy!