Preheat an oven to 350 degrees F (175 degrees C). Lightly grease a 9x13 inch baking dish.
Break spaghetti into 2-inch pieces. Fill a large pot with lightly salted water and bring to a rolling boil over high heat. Once the water is boiling, stir in the spaghetti, and return to a boil. Cook the spaghetti uncovered, stirring occasionally, until it has cooked through, but is still firm to the bite, about 12 minutes.
Drain well in a colander set in the sink.
Combine onion, pimiento, and green pepper with cooked spaghetti, 1/2 cup Cheddar cheese, turkey meat, mushroom soup, chicken broth, salt, and pepper in a large bowl.
Mix lightly and spread the mixture in the baking dish and top with 1/2 cup shredded Cheddar cheese.
Bake, uncovered, in oven for 45 minutes until the casserole is bubbling and cheese topping is melted and browned.
