1. In a casserole, place the salmon and tilapia. Top with garlic, salt and pepper. Followed by celery, lime juice, lemon juice and orange juice to the dish.
2. Refrigerate the dish for 60 minutes.
3. Take out the casserole from the fridge and add in onion, cilantro, parsley and Serrano pepper if desired.
4. Using a spoon or your fingers, push the cilantro and parsley into the liquids of ceviche for marinating.
5. Refrigerate for at least an hour before serving.
6. Serve this delicious Peruvian Ceviche over a large leaf of lettuce with potatoes or sweet potatoes or corn on the cob or even tomatoes.