Heat electric griddle to 350º or a nonstick skillet over medium-high heat.
Brush butter evenly on 1 side of each bread slice. Place 4 bread slices on griddle or in skillet, buttered side down. Top each with 1 1/2 slices cheese, 2 meat loaf slices, and an additional 1 1/2 slices cheese (total of 3 cheese slices on each sandwich). Top with remaining bread slices, buttered side up.
Cook 4 to 5 minutes on each side or until golden. Serve immediately. Garnish, if desired.