Put your serving plate into the refrigerator or freezer to get very cold.
Check to make sure fish fillets do not smell fishy in any way. Check for bones and remove them with pliers or tweezers if necessary.
Cut the fish into roughly 3/4 inch chunks.
Set a metal or glass bowl into another bowl with ice in it to make sure everything stays very cold. Add the diced fish, sliced onion, minced peppers, and chopped cilantro into the ice-cold bowl.
Add the cold leche de tigre and combine mix everything well.
Leche de tigre should coat the fish nicely while still being loose enough to pool at the bottom of the bowl. If it is too thick, feel free to add 1-2 tablespoons of cold water to get the consistency right. The leche de tigre should take care of almost all the seasoning. If you feel it needs a touch more salt or lime juice, add it now.
Serve the ceviche immediately after mixing! Do not allow it to marinate and "cook" in the dressing. Place the ceviche on the chilled plate and allow any excess leche de tigre to pool on the bottom of the plate. Finish with a drizzle of olive oil.