Why Grill Microwaves? 

Traditional microwaves cook food by bombarding it with waves of electromagnetic radiation. These waves target the water molecules in food and heat them to cook the food. Because they have all the features of a regular microwave, grill microwaves can cook in this manner as well. Grill microwaves have an added feature, and use a halogen heat source or conventional heating element in addition to electromagnetic waves. When you use the grilling function, the food is warmed using both methods simultaneously. The food cooks faster than it does on a grill, but supplements the microwave heat with a more traditional heat source capable of browning foods rather than making them soggy.

Grill Marks

Grill microwaves work well for browning and toasting but often don't leave behind the grill marks some cooks crave, even though the cooking method is similar to true grilling. To duplicate grilling, microwaves use a grill rack elevated above a dish that catches drips. This rack, sometimes heated before any food is added, lifts food closer to the grill heating element at the top of the microwave. As the rack heats, it may create marks on your food resembling those on hot dogs and hamburgers grilled outside -- but are often not as dark or pronounced.