Prepare charcoal barbecue for smoking by lighting and waiting for the gray ash to cover at least 90 percent of the coals. Place the wood chips on the coals and wait about 10 minutes before reducing the air flow to make it burn slower.
Arrange the pumpkin halves cut side down on the barbecue surface and close the lid. Slow smoke for 2 hours or less if you prefer them less smoky; as long as they are tender.
Place bacon in a frying pan over medium heat. Cook until browned and crisp. Remove and drain on paper towel.
Once the pumpkin are smoked scoop the flesh out of the skins with a large spoon and transfer to a food processor. Process until smooth adding butter and half of the water.
Transfer to a saucepan and stir in the chicken stock and remaining water.
Season with salt, cumin, parsley and paprika then simmer over low heat for 40 minutes.
To serve ladle soup into bowls and top with a dollop of sour cream, a generous amount of crumbled bacon and coriander. Dust lightly with cayenne pepper.