1. Cook macaroni according to directions- but do not add salt to cooking water. Drain and set aside.
2. Spray casserole dish with nonstick cooking spray.
3. Preheat oven to 350 degrees F.
4. Lightly spray saucepan with nonstick cooking spray. Add onions to sauce pan and saute for about 3 minutes.
5. In another bowl, combine macaroni, onions, and rest of the ingredients, and mix thoroughly.
6. Transfer mixture into casserole dish.
7. Bake for 25 minutes or until bubbly. Let stand for 10 minutes before serving.