If using raw prawns, bring a pan of lightly salted water to the boil, add the prawns and cook for 2–3 minutes until pink and opaque. Drain, then cool under cold running water before peeling and deveining. If you’re using pre-cooked prawns, simply rinse them under cold water, pat dry and cut any large ones into bite-sized pieces.
Finely dice the red onion and cucumber, chop the coriander and, if using, deseed and finely chop the jalapeño. Peel, stone and dice the avocado.
In a large bowl, whisk together the tomato juice (or Clamato juice if you can find it), tomato ketchup, lime juice, hot sauce, salt and freshly ground black pepper until well combined.
Gently fold in the prawns, red onion, coriander, cucumber, avocado and jalapeño, taking care not to mash the avocado.
Cover and chill in the fridge for at least 30 minutes (up to 1 hour) to let the flavours meld and the cocktail cool through.
Give it a final stir, taste and adjust the seasoning if needed. Serve in individual glasses or small bowls with tortilla chips or plain crackers and extra lime wedges.