1. Stir together plums, next 4 ingredients, and 1/4 tsp. salt in a medium bowl.
2. Stir together brown sugar, cumin, and remaining 1/2 tsp. salt in a small bowl. Rub chicken with brown sugar mixture.
3. Cook chicken in hot oil in a grill pan or nonstick skillet over medium heat 3 minutes on each side or until done. Serve with plum mixture.