Cook the bacon strips in a skillet over medium heat until crispy, about 6-8 minutes. Remove and drain on paper towels, then chop into smaller pieces.
Spread butter evenly on one side of each bread slice; these will be the outer sides for grilling.
Place one bread slice, buttered side down, on a heated skillet or griddle over medium heat.
Layer a slice of cheese over the bread in the skillet, followed by some shredded lettuce, chopped bacon, and another slice of cheese on top to enclose the fillings.
Top with the second bread slice, buttered side up, and gently press down to help everything stick together.
Cook the sandwich for about 3-4 minutes on each side, until the bread is golden brown and crispy, and the cheese has melted inside. Carefully flip with a spatula to avoid spilling the fillings.
Once both sides are golden and crispy, remove the sandwich from the skillet and let it rest for a minute before slicing.
Slice the sandwich in half diagonally, revealing the gooey cheese, crisp bacon, and fresh lettuce inside.
Serve immediately while warm, enjoying the crispy exterior and melted cheese with the fresh, crunchy filling.
