Cut the fish fillets into small, bite-sized cubes.
Place the fish in a bowl and cover with the lime or lemon juice. Let it marinate in the refrigerator for at least 2-3 hours, or until the fish is opaque and "cooked" by the citrus juice.
In a separate bowl, combine the finely chopped red onion, red chilies, diced tomato, diced cucumber, and chopped cilantro or parsley.
Add the marinated fish to the vegetable mixture.
Stir in the coconut milk and season with salt and black pepper to taste.
Mix everything gently until well combined.
Enjoy your meal!