In a large glass bowl, cover the diced fish with the lemon juice and lime juice.

Stir, and add half the onion.

Cover and refrigerate for 4 to 6 hours, or until the fish is completely opaque.

Stir halfway through the marinating time to make sure the citrus is evenly “cooking” the fish.

Remove the fish from the refrigerator, drain, and discard the marinade.

In a clean bowl, stir to combine the fish with the remaining onion, the garlic, and the jalapeño.

Season with salt and pepper.