An indirect-heat fire in a gas grill is ideal for cooking whole birds or roasts. Cooking them on the grill can be even better than roasting them in a conventional oven.
Light grill. After preheating the grill to at least 350˚, create two heat zones by turning off one heat element. For a three-burner grill, turn off the middle burner.
For even cooking, tie or truss large cuts of meat or whole birds before grilling. Place the food over the area with no heat.
Cover the grill and let the food cook in the circulating heat (similar to oven roasting). Turn the food periodically to ensure that it’s cooking evenly and is not browning too fast.