When you want to cook a dish in the microwave and you only have directions for cooking it in the oven, you will need to convert the regular oven cooking time to microwave cooking time. A device in the microwave called a magnetron creates a combination of high-frequency waves that cause the molecules in the food to move very fast and create the heat that cooks it. Food cooked in a microwave heats up much faster than food cooked in a regular oven. Some recipes convert easily from regular oven to microwave cooking time, while others will require you to vary the microwave cooking time until you find what works best.
Divide the provided regular oven cooking time by four. For example, if your regular cooking time is 40 minutes, divide 40 by 4 to get 10 minutes. This is your microwave cooking time.
Use this microwave cooking time instead of the regular oven cooking time. Monitor the cooking progress and stop the microwave regularly during the last few minutes to check the food so that it does not overcook.
Add additional minutes to the microwave cooking time if necessary. As the end of the converted cooking time approaches and you notice that part of the food remains cold, add a couple minutes to the microwave cooking time until the food is cooked thoroughly.
Allow the food to remain in the microwave for a few minutes after the microwave has stopped. According to the University of Tennessee Agricultural Extension Service, "Standing time is necessary to allow foods to complete cooking in the center without overcooking on the edges." Let covered meat stand for 10 to 15 minutes. Let covered casseroles and vegetable dishes stand for 5 to 10 minutes.
Note the microwave cooking time on your recipe card or in your recipe book. This way you'll only have to convert the oven cooking time once.
Find a similar recipe in the cookbook that your microwave came with. Follow that suggested microwave cooking time as an additional guide.