Heat oven to 350°F. Spray 8-inch square (2-quart) glass baking dish with cooking spray.
In 3-quart saucepan, heat water and butter to boiling over medium-high heat. Remove from heat; stir in potato mix, and let stand 1 minute. Stir in sour cream and 1 cup of the cheese until completely blended. Spoon mixture into baking dish.
In medium bowl, stir together chicken, BBQ sauce and ¼ cup of the green onions. Spoon chicken mixture over potatoes; top with bacon and remaining ½ cup cheese.
Bake 22 to 25 minutes or until cheese is melted and edges are bubbly. Top with remaining ¼ cup green onions.