A microwave oven includes a cabinet that defines a cooking chamber and a steam generator within the cooking chamber. The steam generator includes a disk-shaped main body with a water storage volume internal to the main body. The steam generator also includes a connector in operative communication with a motor of the microwave oven. The motor is operable to rotate the disk-shaped main body during a cooking operation of the microwave oven. The steam generator also includes a plurality of vents positioned above the water storage volume. The vents direct steam from the water storage volume into the cooking chamber of the microwave oven appliance during the cooking operation of the microwave oven appliance.