This crowd-pleasing party sandwich works on your schedule. You can prepare and bake it all at once for a party, or assemble the sandwiches the night before, and then bake them when your guests are ready to eat. Perfect for Game Day!
Sprinkle chicken with garlic salt and pepper. Brush both sides of onion slices with oil. Cook in a grill pan over medium heat for 12 to 15 minutes or until chicken is no longer pink (170 degrees F) and onion is tender and lightly charred, turning once halfway through grilling. Remove from grill. Thinly slice chicken. Separate onion into rings.
In a small bowl combine mayonnaise and mustard. Halve bread loaves horizontally. Hollow out each half, leaving a 3/4-inch shell. Spread the insides of bread halves with mayonnaise mixture. Layer the bottoms with chicken, onion, bacon, and cheese. Replace the tops; press down firmly. Tightly wrap each sandwich in foil. If you like, chill up to 24 hours.
When you are ready to serve, remove sandwiches from refrigerator and preheat oven to 350°F. Bake wrapped sandwiches for 10 minutes, or until heated through. Cut each sandwich into four portions, and secure each with a wooden pick before serving.