1. Combine raspberries and lemon juice in food processor fitted with metal blade; process until smooth. Refrigerate until ready to serve.
2. Combine brown sugar, cinnamon and rum, if desired, in medium bowl; coat peach halves with mixture. Place peach halves, cut sides up, on foil. Dot with butter. Fold foil over peaches, leaving head space for steam; seal foil. Grill over medium coals for 15 minutes.
3. To serve, spoon 2 tablespoons raspberry sauce over each peach half. Garnish with fresh mint sprig, if desired.