Preheat oven to 450 degrees F. In a large microwave-safe bowl combine vegetables, gravy, and the 1 teaspoon sage. Cover with vented plastic wrap; microwave on high (100 percent power) for 5 minutes. Add turkey; cover and microwave 4 to 6 minutes more or until stew is heated through and vegetables are tender, stirring occasionally. In a small bowl combine pepper and nutmeg; set aside.
Spoon stew into four 14- to 16-ounce casseroles. Top with apple and, if desired, fresh sage. Drizzle with melted butter and sprinkle with nutmeg mixture. Bake uncovered, for 10 minutes or until bubbly and apple slices begin to brown.