Heat oven to 400 degrees. Spray 13×9 inch (3 quart) glass baking dish with cooking spray.
In large bowl, mix chicken, poultry seasoning, garlic powder, sour cream and milk. Season well with salt and pepper. Fold in cheese and onions. Spoon mixture into baking dish.
In medium bowl, stir together topping ingredients just until blended. Spread batter evenly over chicken mixture.
Bake about 30 minutes or until toothpick inserted in center of topping comes out clean. Sprinkle with additional chopped green onions, if desired.
