To cook the mini nut roasts from frozen, either defrost them in the fridge for about 4 hours, then cook them in the preheated oven at 200℃ (390℉) for 20 to 25 minutes, as usual. To cook straight from frozen, allow to cook for a total of 30 minutes. If the nut roast was already cooked before freezing, you can cook at a slightly lower temperature of 180℃ (350℉). A splash of water helps to keep it moist.