While you absolutely shouldn’t attempt to cook a turkey from frozen, for some pre-cooked leftovers such as portions of stews and soups, official advice from the USDA (United States Department of Agriculture Food Safety and Inspection Service) says it’s fine to reheat directly from the freezer. You can do this in the oven, on the hob or in the microwave but it will, of course, take longer than thawed foods. As always, check your food is piping hot and cooked evenly all the way through.