Mix onion, lime zest and juice in a small bowl and let sit while you prepare other items.
Mix shrimp, tomatoes, jalapeno, garlic, salt, and pepper in another bowl.
Whisk Clamato or tomato juice/sauce, ketchup, cilantro and hot pepper sauce in a bowl, add lime and onion mixture and combine well, then pour onto shrimp mixture and stir until everything is combined.
Gently fold in the chopped avocado, cover and chill in the refrigerator for at least 1 hour. Two or more hours is better. Give the sauce a taste before chillin to make sure it has enough of everything for your taste.
Eat within 24 hours, serve in a pretty glass with a side of tortilla chips or saltine crackers.