Spread mayonnaise on one side of each bread slice.
Layer turkey, cheddar, bacon, and spinach on the unbuttered side of one slice.
Top with the second slice of bread, mayo side in.
Spread butter on the outer sides of the sandwich.
Heat a skillet over medium heat.
Cook the sandwich for 3-4 minutes per side until golden brown and the cheese is melted.
Slice in half and serve warm.