Start by cutting ½-inch cubes of fresh white fish like tilapia or halibut. Place the diced fish into a glass bowl, ensuring it's evenly distributed for marinating.

In a pot, bring salted water to a boil and add shrimp. Cook for 2-3 minutes until the shrimp turn pink and opaque. Once done, drain the shrimp and cool them under cold water before chopping into smaller pieces. Add the chopped shrimp to the bowl with fish.

Cover the seafood mix with freshly squeezed lime and lemon juice, ensuring every piece is submerged. Refrigerate and let it marinate for 30 minutes to 1 hour.

After marinating, stir in chopped red onion, tomato, cucumber, and jalapeño into the bowl.

Pour in some orange juice to sweeten the mixture, then season with salt and pepper to taste. Mix everything gently but thoroughly.

Just before serving, gently fold in diced avocado to maintain its integrity.

Serve the ceviche chilled in decorative bowls, garnished with lime wedges and extra cilantro if desired.