1. In a large skillet, saute onions, celery, and bell pepper in the margarine.
  2. In a large bowl, combine onion-pepper that was just cooked, and the seasonings,spaghetti, chicken, sour cream, and alfredo sauce and mix well.
  3. Fold in peas and half of the mozzarella cheese.
  4. Spoon into greased 10×14 inch deep casserole dish, and bake covered at 350 degrees for 45 minutes.
  5. Remove from oven and sprinkle remaining cheese over the dish.
  6. Return to oven for 5 additional minutes.