Bring a large saucepan of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain and set aside.
Preheat oven to 190 degrees C.
Meanwhile, melt butter in a large saucepan over medium heat. Add mushrooms, onion and capsicum and saute until tender. Stir in cream of mushroom soup, chicken stock and water and cook, stirring, until heated through. Stir in pasta, Cheddar cheese, peas, sherry, Worcestershire sauce, salt, pepper and chicken. Mix well and transfer mixture to a lightly greased 20x30cm baking dish. Sprinkle with Parmesan cheese and paprika.
Bake in the preheated oven for 25 to 35 minutes, or until heated through.