Combine dry milk, evaporated milk, and guava paste in a medium saucepan over low heat. Cook 15 minutes or until guava paste dissolves, stirring constantly.
Combine vanilla, salt, and yolks in a large bowl, stirring with a whisk. Gradually add milk mixture to bowl, stirring constantly with a whisk. Return mixture to pan. Cook over medium heat 10 minutes or until mixture thinly coats the back of a spoon or registers 160° on a thermometer, stirring constantly with a whisk (do not boil). Remove from heat, and stir in reduced-fat milk. Immediately pour mixture into a bowl. Cover and chill 3 hours. Pour mixture into the freezer can of an ice-cream freezer; freeze according to manufacturer's instructions. Stir chopped ginger into mixture. Spoon gelato into a freezer-safe container. Cover and freeze 2 hours or until firm. Garnish with additional ginger and mint, if desired.