1 loaf Italian bread (10 to 12 inches)
1 Tbsp mustard
6 slices cheese (swiss, mozzarella, cheddar, etc.)
3/4 lb thinly sliced fully cooked deli meat (ham, pastrami, turkey, etc.)
Heat campfire (or grill). Spray 25×18-inch sheet of heavy-duty foil with cooking spray. Without cutting all the way through, cut loaf of bread into 12 (3/4-inch) slices, cutting to within 1/4 inch of bottom.
Spread every other slice of bread with mustard, creating 6 sandwiches. Fold each slice of cheese in half diagonally; tuck each into sandwich. Divide ham evenly among sandwiches, tucking in to fit. Place loaf on center of foil. Seal edges, making tight 1/2-inch fold; fold again, allowing space for heat circulation and expansion.
Place the tin foil package at the edge of the fire. Do not place it directly in the flame. The goal is not to burn it to a crisp, but to toast it slowly with the heat from the fire. Let it sit for a few minutes (about 5) and flip. You can periodically check to make sure it isn't burning.
Sandwich is done when the bread is lightly browned and contents are warm (cheese is melted). To serve, open packet carefully to allow steam to escape. Remove foil from loaf; pull apart sandwiches.