Assemble the sandwich: Spread the butter on each bread slice. Lay out 2 slices of bread. Top each slice with ½ ounce of fontina cheese. Layer on the peach slices and 2 pieces of bacon. Then top with another ½ ounce of fontina cheese. Cover each sandwich with the other slice of bread.
Cook and serve: Spray a large skillet or sauté pan with cooking spray and place over medium-high heat. Once heated, place the sandwiches in the pan, cooking for about 3 minutes on each side or until the bread is toasted to your liking and the cheese is melted.