Bring a large pot of lightly salted water to a boil. Heat the oil in very large skillet over medium-high. Add the onion, garlic and red pepper and cook 2-3 minutes. Add the halibut and prawns and cook, gently stirring, 2-3 minutes more. Add the wine and bring to a simmer. Add the mussels and cover and cook until they just open. Transfer seafood mixture to a large bowl. Cook pasta in boiling water.
Add the citrus juice and zest to the skillet and cook until almost evaporated. Add the cream and bring to a boil. Return the seafood to the skillet. Stir in dill, salt and pepper. Toss in the cooked pasta and serve.