Steps:

• Place clam juice and oregano in a saucepan; bring to a boil over medium-high heat. Add shrimp and stir just until shrimp turn pink and are not quite cooked through, about 2 minutes. Transfer shrimp to a bowl with a slotted spoon. Reserve liquid. Let shrimp cool to room temperature.
• Place chopped tomatoes, cucumbers, celery, red onion, and jalapenos is a mixing bowl. Add ketchup, cooking liquid from the shrimp, lime juice, cilantro, and hot sauce. Gently mix until ingredients are well blended.
• Chop shrimp into bite-size pieces, leaving a few whole for garnishes. Stir chopped pieces into the vegetable mixture. Wrap mixing bowl with plastic wrap. Place reserved shrimp in a bowl; wrap with plastic wrap. Refrigerate shrimp cocktail and reserved shrimp until thoroughly chilled, 2 to 3 hours.
• If mixture seems a bit thick, add a little tomato juice or pickle juice. Stir in avocado cubes. Serve, if possible, in clear glass bowls. Top with reserved whole shrimp and some cilantro leaves.