In a glass or ceramic bowl, combine the diced fish with fresh lime and lemon juices. Ensure all pieces are submerged in the citrus juice. Refrigerate for exactly 10-15 minutes—this brief window creates the perfect balance between flavor development and texture.
While the fish marinates, prepare your vegetables—dice the red onion, jalapeño, and cilantro. Have them ready alongside your measured olive oil, salt, and pepper.
After the marination period, add the diced vegetables, olive oil, salt, and pepper to the fish. Gently fold everything together with a rubber spatula, being careful not to break apart the delicate fish pieces.
Just before serving, fold in the diced avocado. Taste and adjust seasoning if needed, adding more salt, lime juice, or jalapeño according to your preference.
Serve immediately in chilled bowls or glasses, garnished with additional fresh cilantro. Accompany with tortilla chips, tostadas, or lettuce cups for a complete presentation.