While technically, you can melt cheese on bread in the microwave, I wouldn't recommend it because the bread will get soft and soggy and you won't achieve that crispy texture of a classic grilled cheese. And make sure to also never reheat a grilled cheese in the microwave! You will end up with a greasy mess and a soggy exterior. You can reheat a grilled cheese on the stovetop or in the oven or toaster oven, and that's how you want to make a grilled cheese as well. To reheat in the oven, place the each grilled brie and apple sandwich on a sheet pan and bake at 325 degrees until the cheese is melty. To reheat in a skillet, add it to a pan over medium-low heat with a lid over top. Cook until the cheese melts and the bottom gets crispy again.