Cook onions and bacon in skillet on medium heat 10 to 12 min. or until onions are tender, stirring frequently.
Remove from heat.
Heat oven to 400F. Unroll pie crust on baking sheet.
Mix cream cheese and sour cream until blended; spread onto crust. Spoon onion mixture over cream cheese mixture; spread to within 2 inches of edge of crust.
Sprinkle with Swiss cheese. Fold edge of crust over filling, leaving opening in center and pleating edge of crust as necessary to fit.
Bake 12 to 15 min. or until crust is lightly browned. Cool slightly.