Preheat the oven to 375 degrees F.
In a small bowl, mix the apple with the brown sugar. Set aside.
Pierce the squash several times with a sharp knife so that steam can get out during cooking. Microwave on high for 3 minutes to soften the squash.
Place the squash on a cutting board and cut in half. Scrape the seeds out of the center of each half and throw them out. Fill the hollowed squash with the apple mixture.
Place the squash on a baking pan. If the squash can sit upright, cook it upright and tent aluminum foil over the top. If it can’t stand upright, cook the squash upside down.
Cook the apple-filled squash for 30 to 45 minutes or until very soft.
Transfer the squash to a serving dish. Top each half with 1 teaspoon margarine and serve right away.