Mexican Ceviche

Name: Mexican Ceviche
Cuisine: Mexican, Latin American, American
Ingredients: 500g fresh white fish fillets (sea bass, tilapia, or snapper), finely diced; 1/2 cup freshly squeezed lime juice (about 6-7 limes); 1/2 cup freshly squeezed lemon juice (about 4-5 lemons); 1 small red onion, finely diced; 1 medium tomato, finely diced; 1 small cucumber, peeled, seeded, and diced; 1-2 serrano or jalapeño chilies, finely minced (adjust heat to taste); 1/2 cup fresh cilantro, chopped; 1 avocado, diced; Salt and black pepper to taste; Tortilla chips or tostadas for serving; Lime wedges for garnish