Place chicken in a large Dutch oven; add water to cover. Bring to a boil; cover and simmer 1 1/2 hours or until chicken is tender. Remove chicken from Dutch oven, reserving 2 cups broth. Bone chicken; chop meat, and set aside
Bring water and 1 teaspoon salt to a boil in a heavy saucepan. Gradually stir in spaghetti; return water to boil. Boil 9 to 11 minutes; drain and set aside.
Add onion, green pepper, curry powder, remaining salt, and pepper to reserved broth in Dutch oven. Bring to a boil; cover and simmer 10 minutes or until vegetables are tender. Add tomatoes, mushrooms, and pimientos; cook, uncovered, until thoroughly heated.
Spoon half of cooked spaghetti into a buttered 2 1/2-quart casserole; top with half each of chopped chicken, tomato mixture, and shredded Cheddar cheese. Repeat layers with remaining spaghetti, chopped chicken, and tomato mixture. Bake at 350° for 50 minutes. Add remaining Cheddar and Parmesan cheese, and bake an additional 10 minutes or until cheese melts.