Preheat oven to 450°.
Tear off 4 (12- x 18-inch) foil sheets. Place 1 chicken breast in center of each foil sheet.
Stir together peppers, beans, corn, and fajita seasoning, and spoon evenly on top of chicken.
Bring up 2 sides of each foil sheet, and double fold with about 1-inch-wide folds. Double fold each end to form a packet, leaving room for heat circulation inside packet. Place packets on a baking sheet.
Bake at 450° for 22 minutes or until chicken is done. Open foil packets carefully, allowing steam to escape. Serve over lettuce on individual serving plates with desired toppings. Garnish, if desired.