Light the barbecue half an hour before you begin cooking.
In a bowl, mix together the brown sugar, ground ginger and grated nutmeg until well combined.
Make a deep incision lengthways down the curved side of each banana, from stalk to base. Gently open the bananas up and sprinkle the sugar and spice mixture underneath the skin of each banana.
Place two slices of butter into the incisions made in each banana, then squeeze in the lime juice.
Close the skin around the bananas and wrap them in aluminium foil.
When the flames from the barbecue have died down and the coals are ash-white, place the foil-wrapped bananas onto the grill and cook for 10-12 minutes, turning them occasionally with tongs, or until the bananas are soft when squeezed with the tongs. Remove the foil-wrapped bananas from the heat and set aside to cool slightly on serving plates.
When the foil is cool enough to handle, open the banana parcels and discard the foil. Serve the bananas with a dollop of whipped cream or a scoop of vanilla ice cream.