Peel carrots and potatoes; cut as for French fries. Cut peeled onions into rings. Cut four squares of aluminum foil. Arrange layers of potato strips, carrot strips and half of the onion rings on each piece of foil. Season with salt and pepper; place pat of margarine over each. Place chicken breasts over vegetables on each square. Spread 2 to 3 tablespoons of soup over each chicken breast; top with remaining onion rings. Sprinkle with salt and pepper. Place pat of butter on top. Seal packets; place on baking sheet. Bake at 325 for about 1 hour or until chicken is tender.