These sandwiches get prepped ahead of time and wrapped in foil so you can roast them on a grill or directly on the embers of a campfire.
Spread one side of each slice of bread with mustard, and assemble 8 cheese sandwiches. Wrap each in foil.
Place sandwiches on a medium-hot grill. Roast for about 5 to 7 minutes on each side, until bread is golden brown and cheese is completely melted; serve immediately.