Sweet potatoes have high water content; thus they take longer time when defrosting them compared with other vegetables like peas or beans (in which case it's recommended not to leave them overnight) so make sure not only how long they'll take but also how quickly they should reach room temperature if time is not an issue for you then keep them on room temperature until they feel softer then continue cooking using usual methods but if you're trying something different like grilling them then wrap them in aluminum foil then wrap again tightly so that moisture won't escape but still allow ventilation so that condensation will form around them so as soon as condensation appears make sure that sweet potatoes get thoroughly cooked then unwrap from foil/bag they should already feel soft after all this method won't work for sweet potatoes cooked using traditional method i .e baking because baking takes longer time but not necessarily more tender as compared with steaming or boiling methods which are quicker than baking but still can't give same tender results as compared with ro