Cook spaghetti according to package direction to al dente (do not overcook it!) Then drain in a colander, rinse with cool water and drizzle with a little olive oil to keep from sticking. While the pasta is cooking, mince bell peppers and onion.
In a large bowl mix together cooked pasta, chicken, cream of chicken soup, bell peppers and onions, seasoned salt, pepper, cayenne pepper, chicken broth, and 2 cups of the shredded cheese. Toss until well-mixed.
Spray a 9 x 13-inch casserole dish with nonstick cooking spray. Pour spaghetti mixture into dish and spread out evenly. Top with remaining cheese, cover and bake for 45 minutes. Let stand 5 minutes before serving.