Stir the seafood mix and lime juice together in a large, non-metallic bowl; let stand 10 minutes. Fold in the diced tomatoes and onion; cover, and refrigerate 30 minutes. Whisk together the Worcestershire sauce, hot pepper sauce, tomato paste, cayenne pepper, cumin, chili powder, and salt in a small bowl. Cover, and refrigerate 30 minutes.
After 30 minutes, gently stir half of the tomato paste mixture into the seafood mixture. Cover the remaining tomato paste mixture and the seafood mixture. Return both to the refrigerator for 30 minutes.
After another 30 minutes, gently stir the remaining tomato paste mixture into the ceviche, cover, and refrigerate another 30 minutes.
Gently stir the cilantro and diced avocado into the ceviche before serving.