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 100 percent power (high) for 5 minutes. Add chicken; cover and microwave for 4 to 6 minutes more or until stew is heated through and vegetables are tender, stirring occasionally.
Meanwhile, 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; sprinkle with nutmeg mixture.
Bake uncovered, about 10 minutes or until bubbly and apple slices begin to brown.