1) In a medium saucepan place the ginger beer, Worcestershire sauce, tomato ketchup, apple cider vinegar, hoisin sauce, spice powder, orange juice, garlic, lime juice, onion powder, brown sugar, salt, honey and pepper. Bring to a simmer on low heat for 15 minutes or until thickened. Add the chicken and keep warm.
2) Preheat the oven to 210C/Gas 7.
3) In a small skillet, caramelise the onion with the olive oil and sugar.
4) In the bowl of a food processor combine the flour, brown sugar, baking powder, bicarbonate of soda and salt and pulse to combine. Add the butter and pulse until it resembles coarse crumbs. Remove the contents of the food processor to a medium bowl. Fold in the bacon and onion.
5) Combine the sweet potato puree and buttermilk in a separate bowl. Pour into the dry ingredients and combine to form a soft dough.
6) Place the dough on a floured surface and pat into 2 1/2-cm thickness. Cut out the biscuits with a 10-cm cutter and arrange in a buttered skillet. Place into the preheated oven for 25 minutes or until golden brown. Allow the biscuits to cool slightly before making the sandwich.
To assemble, split a cooled biscuit in half. Place a generous 1/2 cup of barbecue chicken on the bottom half of the biscuit and top with the other biscuit half.