Cook bacon over medium-high heat until crisp, 6 minutes. Drain excess grease on paper towel, then wipe pan and reduce to medium heat.
Spread butter on one side of each slice of bread. On the non-buttered side of one slice, place turkey, bacon, avocado and cheddar, then close sandwich.
Place sandwich in pan; cover and cook until golden brown, 3 to 4 minutes. Flip, and cook the other side until cheese is melty and bread is golden brown, 2 minutes more.
Slice in half and serve.
