Bring the pan of prawn stock up to a boil, and add spaghetti. Meanwhile, finely chop the onion and fry in a wok or deep frying pan. Add garlic when the onions soften, and fry for a further couple of minutes. Add a glug of cheap white wine, and cook until reduced. Add half of the sliced tomatoes, the parsley, lemon zest and dried oregano. Add a ladleful of the spaghetti cooking water and cook until slightly reduced. Then add all of the prawns, the smoked paprika and the rest of the tomatoes. Add salt and pepper to taste.