In a saucepan, bring clam juice and oregano to a boil over medium-high heat.

Add shrimp and cook for about 2 minutes until they turn pink (they won't be fully cooked). Remove shrimp with a slotted spoon and let them cool to room temperature, reserving the liquid.

In a mixing bowl, combine tomatoes, cucumbers, celery, onion, and jalapeños. Gently mix in the reserved cooking liquid, ketchup, lime juice, 2 tablespoons of cilantro, and hot sauce until well combined.

Place four whole shrimp in a small bowl, cover with plastic wrap. Chop the remaining shrimp into bite-sized pieces and add them to the vegetable mixture. Stir to combine and cover with plastic wrap. Refrigerate both bowls for 2 to 3 hours until thoroughly chilled.

When ready to serve, stir in the avocado into the shrimp cocktail. Divide the mixture into four glass bowls, top each with a chilled whole shrimp, and garnish with cilantro before serving.