Mix either 2 tbsp. baking soda or several tbsp. lemon juice to a cup of water, or mix white vinegar half and half with water in a microwave-safe container.
Turn the microwave on high long enough to bring the liquid to a boil.
Keep the door to the microwave shut for a few minutes after the liquid has boiled to give it time to neutralize odors and soften any food matter in the microwave. Allow the liquid to cool down before handling.
Remove the cooled vessel from the microwave. Remove the liner glass and the runner it sits on and wash them in hot, soapy water in the sink. Dampen a cleaning cloth with the homemade mixture and wipe down the interior. Clean all surfaces, including the ceiling of the microwave and the door interior.
Wash and rinse until all the food particles are gone and the microwave is free of odor, and then replace the runner and glass liner after drying thoroughly.