Ceviche is a South American dish of fresh fish cured in citrus juice, with various vegetables. We found a good recipe from Marco Hernandez (OverlandX) on YouTube. His recipe is too spicy for Leif's gastric reflux, though, so we've cooled it down. It's pretty easy to prepare, mainly requiring cutting up the fresh ingredients and then letting them sit for a while.
Choose a nonmetallic bowl or dish large enough to hold all the ingredients. All ingredients will be diced to about the same size, ¼ inch or 6mm on a side.
Squeeze lemons into bowl. Dice onions about ¼ inch on a side, and add to lemon juice in bowl. Dice the tilapia about ¼ inch on a side, and add to lemon juice in bowl. Mix it up thoroughly to make sure the tilapia is all in contact with the lemon juice; add more lemon juice if needed.
Slice the tomato and cucumber, and remove the seeds. Dice both about ¼ inch on a side, and add to lemon juice mixture in bowl. Chop the parsley and add to the bowl. Mix; add salt and pepper to taste; our taste runs to about a quarter teaspoon of salt and a small sprinkling of black pepper.
Peel and dice the avocado about ¼ inch on a side, and add to the mix in the bowl. Mix gently so that the avocado doesn't get crushed.
Allow to soak for at least half an hour to let the fish cure, then serve cold. It's pretty good then, but we think it tastes better if allowed to sit longer, and best if allowed to sit overnight in the refrigerator. Refrigerate any leftovers.
For more flavor and heat, add 2 fresh Serrano chilis. Slice them open, remove the seeds, and dice to about ¼ inch on a side. Add these before the tilapia, letting them soak in the lemon juice for best flavor.
For a slightly different flavor, substitute cilantro for the parsley. If you're one of the unlucky ones for whom cilantro tastes distinctly soapy, you may want to use the parsley.
For more flavor and heat, add some hot sauce. Marco recommends 2-3 spoonfuls each of Inca's Food Aji Rocoto and Aji Amarillo, adding them along with the salt and pepper.
One way to serve is on a tostada with mayonnaise.