Heat oven to 375°F. Unroll pie crust on ungreased cookie sheet. Spread sour cream in center of crust, leaving 1 1/2-inch border around edge.
Microwave potatoes as directed on bag. Transfer to medium bowl; toss with cheese. Spoon potato mixture on top of sour cream. Sprinkle with bacon. Fold edge of crust over filling, pleating crust as necessary.
Bake 25 to 30 minutes or until crust is golden brown. Let stand 5 minutes. Top with green onion.