PREHEAT oven to 400°F. Sprinkle chicken with seasoning mix. Place 1/2 cup of the potatoes on center of each of four large sheets of heavy-duty foil; top each with chicken, salsa and cheese.
BRING up foil sides. Double fold top and both ends to seal each packet, leaving room for heat circulation inside. Place in 15x10x1-inch baking pan.
BAKE 30 to 35 min. or until chicken is cooked through (165°F). Remove packets from oven. Let stand 5 min. Cut slits in foil to release steam before opening. Serve with sour cream.