Preheat the oven to 375°F. Cook the spaghetti al dente in salted water according to package directions. Drain well, do not rinse.
Meanwhile, in a medium skillet, melt the butter over medium heat. Add onion, garlic, and bell pepper can cook until tender. Stir in the flour and Italian seasoning and cook for 1-2 minutes.
Gradually add the broth and cream, a bit at a time, stirring until smooth after each addition. Bring to a boil and let boil 1 minute or until thick and bubbly.
Remove from heat and whisk in parmesan cheese, 1 cup cheddar cheese, and salt and pepper.
Combine spaghetti, chicken, cream sauce, and canned tomatoes. Mix well. Spread in a greased 9x13 dish.
Top with remaining 1 cup of cheddar cheese and bake for 25-30 minutes or until hot and bubbly.
