Drain liquid from beets into measuring cup. Add enough water so that beet liquid measures 2/3 of a cup. Set aside.
Mix together cornstarch, sugar and salt in a deep, 1 1/2-quart, heat-resistant, non-metallic casserole.
Gradually add beet liquid and vinegar to cornstarch mixture. Stir until smooth.
Heat, covered, in Microwave Oven 1 1/2 minutes or until beet liquid comes to a boil. Stir.
Boil beet liquid for an additional 1 minute. Stir after 30 seconds.
Add beets and heat, uncovered, in Microwave Oven 3 minutes or until beets are heated through.