Begin by cleaning your fish and seafood. Most supermarkets will have the fish already skinned and bones picked, but still check the flesh to make sure there are no other bones that need removal.
Dice the fish into bite-size pieces and place them in a bowl. For the shrimp, depending on the size cut either in half or in thirds and add to the bowl.
Dice onion and add to the bowl. Crush and mince the garlic and add to the bowl.
Add oil and lemon-lime juices. mix contents thoroughly, make sure liquid is covering the fish and seafood. Add more juices if needed.
Season with salt, pepper, and cumin. If your fish is fresh, and you trust your source, you can serve immediately. Otherwise, let the fish and seafood marinate in the juices for a few hours. I let mine marinate for 6 hours. Made it in the morning and ate it that evening.
let's drain the ceviche, but reserve the liquid. While the excess liquids drain, grab another bowl. Option to dice the other half of the onion and add it to the bowl. Dice the avocado and the plum tomato. Add the parsley and cilantro. If you are using the spicy peppers or jalapeño dice it and add to the mixture. Add the drained ceviche to the bowl and a squirt of olive oil. Mix. If the mixture seems too dry, add a little of the reserved liquid to moisten and serve.