Preheat oven to 375°F. Cook spaghetti al dente and drain well.
Boil chicken, cool, and shred. (or use your rotisserie or leftover chicken)
Cook onion and bell pepper in oil until tender. (I cook this is a large enough skillet that will hold all the ingredients to keep from dirtying a bowl.)
To the onions and peppers, add pimentos, cream of chicken soup, and cream cheese. Heat until cream cheese melts. Remove from heat, add parmesan cheese and 1 cup cheddar. Mix until smooth and melted.
Season with celery seeds, salt, cayenne pepper, and black pepper.
Combine spaghetti, chicken, and cream sauce. Mix well. Spread in a greased 9x13 dish. Top with remaining cheddar cheese and bake 25-30 minutes or until hot and bubbly.