Never use packaging cartons for cooking unless the package directs you to do so. Many plastic containers in which foods are sold are designed for cold storage and are not suitable for cooking or reheating. Chemicals from them can be absorbed into foods at high temperatures. Cut food into uniform sizes so it will cook evenly. If foods are different sizes, arrange them in microwaveable dishes so thick parts are toward the outside.
Outer areas receive more microwaves than the center.
For optimal safety, cover the dish with its lid or heavy-duty plastic wrap turned back at one corner. Plastic wrap shouldn't touch the food. Trapped steam will help even the temperature throughout the food, promoting safe cooking. Rotate the dish midway through cooking. If the dish is on a rotating turntable, it's still a good idea to reposition the dish on it.