Plum Sauce: Use side burner or grill. Heat oil in a medium saucepan over medium-high heat. Add onions and garlic and cook until soft. Add ginger, chile pepper, cinnamon and cloves and cook for 2 minutes. Add remaining ingredients and cook until plums are soft and mixture has thickened. Place mixture in a food processor and mix until smooth. Let cool.
Preheat grill. Season chicken with salt and pepper to taste. Grill, on 1 side for 5 minutes, or until golden brown. Turn the chicken over, brush with the sauce and continue grilling for 3 to 4 minutes, turn over and brush with sauce. Continue grilling and brushing with the sauce until the chicken is cooked through, approximately 12 to 15 minutes.