In a 2-quart glass baking dish, combine the olive oil and onion. Microwave on High for 4 to 6 minutes, or until the onion is very tender, stirring once or twice. Add the spinach, salt, pepper, and nutmeg. Stir thoroughly to coat with oil and to break up the mixture a bit. Microwave on high for 2 to 4 minutes, or until the spinach is tender and the mixture is heated through.
This recipe serves 4.