Place a casserole dish or large saucepan over a medium heat with a tablespoon of oil. Add the chorizo, garlic, onion and red pepper. Cook for five minutes, stirring frequently. Add the Cajun and oregano and cook for a minute or two until fragrant.
Add the tinned cherry tomatoes, mustard, cream and water, followed by the orzo. Bring to a boil, then reduce the heat to a simmer and cook for about 10 minutes, add more water if needed. Stir frequently to stop the orzo sticking to the pan.
Stir in the prawns and cook until they are heated through and the orzo is also cooked, about 3 minutes more. Serve up and finish with black pepper and chopped fresh flat leaf parsley.