Follow the steps in order for the best result.
In a bowl, combine the cubed tilapia (or other white fish), chopped garlic, salt, black pepper, chopped cilantro, and chopped habanero pepper (or Aji Amarillo). Mix thoroughly to ensure all ingredients are well combined.
Arrange the thinly sliced red onion on top of the fish mixture. This will allow the onion to infuse its flavor into the ceviche as it marinates.
Pour the freshly squeezed and strained lime juice over the fish and red onion, making sure the fish is fully submerged in the juice.
Cover the bowl and refrigerate for at least 2-3 hours, or until the fish is opaque and 'cooked' by the acidity of the lime juice.
Before serving, gently mix the ceviche to redistribute the flavors. Serve chilled with lettuce, corn, avocado, or other cold salad vegetables as accompaniments.
Note: For the best lime juice, use a juicer that presses the juice out without tearing the membranes of the lime, as this can make the juice bitter.