1) In a large bowl, mix together the oil, chili powder, paprika, sage, mustard, ginger, and cayenne until a paste is formed.
2) Add the chicken pieces and rub the spice paste all over, including under the skin. Cover with cling film and refrigerate for 2 hours.
3) Preheat the grill. Place a rack about 23 centimeters from the grill element.
4)Place the chicken on a foil-lined baking sheet or grill pan. Season the chicken all over with salt and pepper and arrange skin-side down.
5) Grill for 10 minutes, turning the pan occasionally so the meat cooks evenly.
6) Remove the pan from the oven and baste the meat all over with the barbecue sauce, turn the chicken pieces skin side-up and grill, basting and turning the pan occasionally, until cooked through and crispy and the sauce has browned lightly, about 10 minutes more.
7) Transfer to a serving platter and serve immediately.
Quick barbecue sauce
1) Heat the oil in a medium saucepan over medium-high heat. Add the onion and cook, stirring, until lightly browned, about 4 minutes.
2) Add the garlic and crushed pepper and cook, stirring frequently, until fragrant, about 45 seconds.
3) Add the tomato puree and cook, stirring, until lightly browned, about 1 minute more.
4) Add the tomatoes, vinegar, sugar, and salt and bring to a boil. Lower the heat, and simmer, uncovered, stirring occasionally, until deep red in colour and reduced to about 950ml, about 25 minutes.
5) Season with pepper. Use now, or store, covered in the refrigerator for up to 3 days or freeze for up to 1 month.