01 -
In a small bowl, mash the avocado with lime juice until mostly smooth. Stir in red onion, cilantro, salt, and pepper. Set aside.
02 -
Butter one side of each bread slice. On the unbuttered side, layer cheddar cheese, mozzarella, guacamole, and crumbled bacon. Add another layer of cheese and close the sandwich with a second slice of bread, buttered side out.
03 -
Heat a skillet over medium heat. Grill each sandwich for 3 to 4 minutes per side, pressing gently, until the bread is golden brown and the cheese is fully melted.
04 -
Slice the sandwiches in half and serve warm while the cheese is gooey and the guacamole is fresh.