Prep the filling: in a small bowl, toss together cooked chopped chicken and ranch dressing. Stir to combine.
Butter the bread: spread an even layer of butter or mayo on one side of the bread. This will face out.
Assemble the sandwiches: place the buttered side of the bread facing down on your working surface. On the non-buttered side of the bread add a slice of American cheese, chicken + ranch mixture, bacon, ½ cup shredded cheddar cheese, another slice of American cheese, then top with a slice of bread, buttered side facing out. Repeat this for both sandwiches.
Cook low and slow: heat a skillet over medium-low heat. Place the sandwiches in the pan and cook until toasted to your liking, about 3-5 minutes. Flip the sandwiches and continue cooking for another 3-5 minutes, until golden brown.
Rest for 1-2 minutes, then serve.