In a small mixing bowl, combine the sugar, cornstarch, and cinnamon, stirring until the cornstarch is fully distributed.
Arrange the apples in a casserole dish, and cover with the sugar mixture.
Cover, and microwave on high for 5 minutes, or until the sugar is melted. Stir and cook, uncovered, another 4 minutes, or until the apples are soft through the center. They should be fork tender. Stir and stir.