In a small pot melt brown sugar in butter with cumin, and cayenne to make brown sugar mixture.
In a medium bowl combine the sweet potatoes, with the brown sugar mixture, salt and pepper.
Spray the grill.
Place the sweet potatoes on the grill cook for four minutes then flip and cook for an additional four minutes, or until a firm outside and soft inside is achieved.
Place two halves of the marshmallows on each slice of sweet potato and close the lid of the barbecue.
Cook for one minute or until the marshmallow begins to toast on the edges and slightly melts though maintains shape.
To serve place topped sweet potatoes on a platter .
Note: Cooking times and temperatures will vary depending on the size and type of your barbeque.