Start fire in grill, placing rack 10 cm above coals (see note). Melt butter over medium heat in a 1 litre saucepan; add garlic; cook 1 minute, stirring until golden. Remove from heat; stir in lemon juice, lemon peel, salt, and pepper. Pour mixture over chicken breasts in a 13 x 9 x 5 cm baking dish; let stand at least 10 minutes or until the fire is ready. Place sheet of foil on hot grill rack. Remove chicken from marinade, reserving marinade. Arrange breasts, skin side down, on foil. Cook, covered with grill cover, 10 minutes. Turn breasts over; cook, covered, 15 minutes longer until cooked through, brushing occasionally with reserved marinade. One or two minutes before end of cooking time, brush breasts with orange marmalade to glaze. Serve when chicken is golden brown. NOTE: Breasts may be baked in oven. Heat oven to 200ºC . Marinate breasts in baking dish as directed; drain off and reserve marinade. Bake breasts, skin side down, 15 minutes. Turn breasts over, brush with marinade. Cook 10 minutes longer until cooked through. Brush with marmalade; cook 1 to 2 minutes longer to glaze.