Heat oven to 375°F. Spray 13x9-inch (3-quart) glass baking dish with cooking spray. In large bowl, stir sauce mix pouches (from potato mix boxes), boiling water, milk, cream cheese, sour cream, Dijon mustard, salt, pepper, garlic powder and onion powder with whisk. Stir in potatoes (from potato mix boxes), chicken and onions; pour into baking dish. Bake 30 minutes.