Cook the spaghetti according to package directions until al dente.
Drain it and set aside.
In a large skillet over medium heat, sauté onions, mushrooms, and bell pepper until softened.
This should take about 5 minutes.
Add the can of tomatoes, cream of mushroom soup, chicken broth, salt, black pepper, garlic powder, and onion powder to the skillet.
Stir well.
Combine the mixture with the cooked chicken and spaghetti.
Transfer to a greased baking dish.
Sprinkle the shredded cheddar cheese evenly over the top.
Bake in a preheated oven at 350°F for 25 minutes or until bubbling.
Serve hot!