Break up graham crackers and spread them in the bottom of your foil pan. The number of crackers you use will depend on the size of your pan. Two cinnamon graham crackers work well in an 8x8 inch foil pan.
Sprinkle mini marshmallows on top of the graham crackers.
Scatter chocolate chips on top of the marshmallow layer.
Repeat with another layer of graham crackers, mini marshmallows, and chocolate chips.
Add a final layer of chocolate chips on top, along with a few regular-sized marshmallows.
Cover the pan with a piece of heavy-duty foil, wrapping it tightly around the edges of the pan.
Place the pan on a grate over a campfire or on the grill, or in an oven preheated to 350°F.
Cook over coals (preferred over an open flame) for about 10 minutes, or on the grill for about 7 minutes, or in the oven at 350°F for 10 minutes, until marshmallows and chocolate have melted.
Check doneness by lifting a corner of the foil or smelling for melted chocolate. For oven baking, you can move the skillet to a higher rack for 1-2 minutes after baking for extra crispy marshmallows, watching closely so they don't burn.
Carefully remove the pan from the heat, take off the foil, and serve.