Heat grill. In small bowl, combine soy sauce, brown sugar, ginger and garlic powder; mix well. Place chicken on plate. Brush both sides of each chicken breast half with soy sauce mixture. Cover; let stand 15 minutes at room temperature to marinate.
When ready to grill, oil grill rack. Place chicken on gas grill over medium-high heat or on charcoal grill 4 to 6 inches from medium-high coals. Cook 8 to 10 minutes or until chicken is fork-tender and juices run clear, turning once and topping each with pineapple slice during last few minutes of cooking time. To serve, sprinkle with coconut.