Tilapia Ceviche

Ingredients

• 2 pounds tilapia fillets, finely diced* see Cook's Note
• 1 cup lime juice (about 8 large limes)
• 1/2 cup seeded chopped tomato
• 1/2 cucumber, peeled, seeded and finely diced
• 1/2 cup finely chopped onion
• 1/4 cup chopped fresh cilantro leaves
• Salt and freshly ground black pepper
• 1/2 cup clam-tomato juice (recommended: Clamato), optional
• 1 tablespoon bottled hot sauce (recommended: Huichol), optional
• 1 serrano chile, optional
• Grilled Tostadas, recipe follows, or 6 purchased tostadas
• Mayonnaise, for spreading
• 1 avocado, halved, pitted, peeled, and thinly sliced
• 1 lime, cut into wedges