Spray a 2 quart casserole dish or 9x13 pan with cooking spray.
Mix the chicken, potatoes, sour cream, cream of chicken soup and seasonings in a large bowl. Add 1 cup of the cheese and half of the French's onions.
Place mixture in the casserole dish. At this time, the dish can be covered with plastic wrap and placed in the refrigerator and cooked later. If refrigerated, take out and allow to come to room temperature before cooking.
Bake at 350 for 45 minutes or until bubbly and a crust starts to appear on top. Remove from oven and top with remaining cheese and French's fried onions. Bake additional 15 minutes.