Combine fish, onion, and lime juice in a large bowl.
Cover with plastic wrap and chill in the refrigerator until the fish is white throughout, about 15 to 20 minutes.
Remove from the refrigerator and drain, pressing into strainer to remove excess liquid.
Return fish mixture to bowl.
Add the tomato, cucumber, cilantro, and Clamato juice
Season with salt and pepper, to taste.
Notes
The fish is easiest to dice when it is partially frozen; this also makes for a much cleaner presentation. Use a very sharp knife.Optional Garnishes: Lime Wedges, Hot Sauce, Mayonnaise, Sliced Avocado, Grilled or Toasted Corn and/or Flour Tortillas