Roasting is done with dry heat in an open pan in a hot oven, about 450 or higher. It crisps up the exterior of the meat or vegetables while slow cooking the inside. To roast vegetables without oil, stir once in a while to distribute natural juices. However, the temperature for roasting nuts is much lower--use a 160-170 degree oven for 15-20 minutes--to preserve the heart-healthy oils in nuts.