For Ceviche, it is critically important to use the freshest fish possible (ideally sushi/sashimi quality) as it is not cooked with heat. The acidic juice denatures the proteins, changing the fish's texture to cooked, but it does not kill all bacteria, so the quality of the fish should be top-notch.
The Costa Rican version is often less spicy than other versions, focusing more on a fresh lime flavor with plenty of cilantro and bell pepper.
Ensure the fish is perfectly cleaned, deboned, and cut into uniform cubes (about 1-1.5 cm).
Place the fish in a non-reactive bowl. Pour fresh lime juice over it so it is completely submerged. Add salt and pepper.
Refrigerate. Marinate for 20-30 minutes. The fish should turn opaque white – this means it is 'cooked.' (If the fish is thicker, marinate for 45-60 minutes).
While the fish is marinating, finely chop the onion, bell pepper, cilantro, and chili if using.
After marinating, drain about half to two-thirds of the lime juice (this juice is called leche de tigre and is usually diluted in Costa Rica, unlike in Peru where it's served separately).
Add the chopped vegetables to the bowl with the fish.
If using, stir in a quarter cup of Ginger Ale. This helps soften the acidity of the lime and adds a gentle ginger note.
Mix well and check the seasoning. Add salt, pepper, or lime juice if needed.
Chill the Ceviche in the refrigerator for another 5-10 minutes before serving.
Serve the Ceviche immediately to prevent the fish from 'overcooking' in the acid.
Serve in small bowls with tortilla chips or on lettuce leaves. It is often topped with slices of fresh avocado.