Preheat oven to 350 degrees F (175 degrees C).
Cook spaghetti according to package directions, add oil and salt to cooking water. Drain.
In large saucepan or Dutch oven over medium heat, melt butter. Add onion and garlic. Cook, stirring occasionally, 2 minutes. Add soup, broth, seasoned salt and 1 1/2 cups of the cheese. Cook and stir until cheese melts and mixture is smooth. Add spaghetti and chicken or turkey. Mix well. Transfer to 2-quart baking dish. Cover with foil.
Bake at 350 degrees F (175 degrees C) for 30 minutes or until hot and bubbly.
Remove foil. Sprinkle with remaining 1 1/2 cups. cheese. Continue baking 2 minutes or until cheese melts. Sprinkle with parsley and bell pepper.