Place apples in deep 9-inch round microwave proof dish. Squeeze lemon juice over apples to prevent discoloration. In food processor, combine 1 tablespoon apple-juice concentrate, raisins, walnuts, cinnamon, and Sweet'N Low® and process until well mixed. Spoon an equal amount of mixture into center of each apple. Pour remaining 3 tablespoons apple-juice concentrate over apples. Cover with casserole lid or microwave-proof plastic wrap, leaving vent. Cook on high power 5-6 minutes, turning dish if apples appear to be cooking unevenly. Remove apples, leaving juice in dish. To reduce juice, return dish to microwave; cook, uncovered, on high power 4-5 minutes. Spoon juices over apples. Serve warm or cold. Sprinkle each apple with nutmeg, if desired.