Place the chicken breasts, skin side up, in a dish or plastic bag. Season with salt and pepper. Mix together the oil, lemon juice, garlic, and rosemary. Pour the juice mixture over the chicken, and cover or seal bag. Marinate, refrigerated, as long as possible, up to 2 days.
When ready to serve, place the chicken, skin side turned to the heat, under the broiler or on a preheated grill 6 inches from the heat, and cook 15 minutes. Turn; and continue to cook until done, about 15 minutes. The juices should run clear when chicken is pierced with a fork. May be made ahead and reheated, but is best hot off the grill.