Heat oven to 400°F.

Spray 13×9-inch (3-quart) glass baking dish with cooking spray.

Sprinkle chicken with seasoned salt.

In 12-inch nonstick skillet, cook chicken and onion over medium-high heat 4 to 6 minutes, stirring occasionally, until chicken is browned.

Stir in gravy.

Heat to boiling.

Reduce heat to medium-low; cover and cook about 5 minutes, stirring occasionally, until chicken is no longer pink in center.

Meanwhile, place vegetables in colander.

Rinse with hot water until thawed.

Remove chicken mixture from heat.

Stir in vegetables and sour cream; spoon into baking dish.

In medium bowl, mix cornbread mix, milk, butter and egg with spoon just until moistened (batter will be lumpy).

Drop batter by spoonfuls into baking dish, around edges of warm chicken mixture.

Sprinkle cheese over batter.

Bake uncovered 20 to 22 minutes or until cornbread is deep golden brown.

Let stand 5 minutes before serving.