Place the bacon under a preheated hot grill (broiler) and cook for 1-2 minutes or until crispy.
Combine the mayonnaise, garlic, lemon juice, chives and chicken in a medium bowl.
Spread both sides of the bread with butter.
Divide cheese and chicken mixture between 4 slices of bread and top with second slice of bread.
Heat a large non-stick frying pan over low heat and cook the sandwiches (in batches if necessary) for 3-4 minutes per side or until golden and cheese is melted.