Cut squash in half; discard seeds. Place squash cut side down in a microwave-safe baking dish. Add 1/2 in. of water. Microwave, uncovered, on high for 10-13 minutes or until almost tender; drain.
Combine the apple, raisins, cinnamon and nutmeg; spoon into squash cavities. Dot with butter. Microwave, uncovered, on high for 6-8 minutes or until squash and apples are tender. Let stand for 5 minutes before serving.