Providing that you have chosen a cheese appropriate for grilling or baking, it is most likely that the cheese has been covercooked. In fact, cheese needs only to be melted. Do not put it too close to a fierce grill. Once cheese reaches temperatures above 75 degrees C, it is likely to become hard, stringy or chewy, because the heat encourages the proteins, fat and water in the cheese to separate.
For a successful result, try adding an equal quantity of fresh breadcrumbs to the grated cheese.
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